[HD2 Android NAND Development] ph03n!x:
Alright, here is the how-to for those who want to test!!!

Have a read through of the first three posts of the mount /data natively to the EXT partition thread before your start.

While I have been using AOSP based CM/ ICS/ JB ROMs for most part (especially after JB came out), I have realized that Sense-based ROMs benefit the most with this method primarily because they are larger than AOSP ROMs, and all A2SD scripts comes with one issue or other when working with Sense ROMS. After doing this mod, you do not have to worry about how many apps do you have, how much space is left or if /system or /data is big enough or what A2SD scripts should you use.

I am currently testing this in "TBD_SUNDAWG_V15_Lite_Edition_Themed", and want to have a larger group of testers. So here is a step-by-step for those who want to try.

Requirements (VERY IMPORTANT)

The attached zip file containing boot.img, initrd.gz, checksys.sh and updated-script

Some amount of understanding of the ROM's zip package

WinRAR on your computer, Titanium Backup's installation (.apk) on your phone's SD Card (FAT partition)

A MicroSD card partitioned with a FAT partition as the first partition and an EXT partition (ext 2/3/4) as the second partition with at least 1 GB of space

Patience - lots of it!!!

Time - about an hour of spare time, and you are good to start

Here is step-by-step to test this mod. This how to may vary for other variants of @sundawg's ROM-

Use Titanium Backup to backup ALL (both system and user) apps and their data

Go to ClockWorkMod or whatever recovery you are using, take a NANDROID backup - this is your fallback option, so don't miss doing this

Download the attached zip file and extract the contents to your computer (say, to a temporary folder in your desktop - am going to assume you are in Windows. If you are a Tux'er you know what to do already!)

Open TBD_SUNDAWG_V15_Lite_Edition_Themed installation zip in WinRAR - I suggest you have a backup copy of the original ROM

Navigate to the folder named kernel in the ROM's zip, and drag n drop the file named boot.img extracted from the zip file attached to this post

Navigate to the folder named kernel > boot in the ROM's zip and drag n drop the file named initrd.gz extracted from the zip file attached to this post

Drag and drop the initrd.gz you downloaded here (overwriting the initrd.gz that is already there)

Navigate to setup in the ROM's zip

Drag and drop the checksys.sh file extractd from the zip file attached to this post (overwriting the checksys.sh file already there)

Navigate to META-INF > com > google > android

Drag and drop the updater-script file extracted from the zip file attached to this post (overwriting the updater-script file already there)

Navigate to system > etc > init.d

Delete the files named 01remount, 02enableswap, 04apps2sd, 07sdcardspeedfix, 40ext4tweaks. (I am mounting /system in the ramdisk with the noatime and nodiratime option, and /data is mounted (to the EXT partition) with noatime, nodiratime, nodev and nosuid. I first off do want to remount data after Android has started, and 01remount does not do much further than what I already have. I do not recommend having a swap partition in the SD Card after /data is mounted to the EXT partition, read my thread for more explanation. removing the apps2sd is a no-brainer, it is not needed. I have set the SD Card cache size to 2 MB as a part of mounting EXT to /data. There is a detailed write up on choosing optimum cache size in my thread, but for now let it not be played with. 40ext4tweaks is removed for the same reason as the 01remount script).

Copy this modified .zip to the SD Card on your phone

Make sure your phone meets the minimum partition requirements specified for the ROM.

Reboot your phone to Recovery and format all partitions EXCEPT your SD Card

Flashing the ROM and let the phone reboot

Set up your phone like you will normally do

Install Titanium Backup

Restore your backed up user apps and data through Titanium Backup

Restore your backed system app's data alone through Titanium Backup

Check the internal space - and report back your experience!!!

If you are familiar with QtADB, you can use it to monitor the installation and the first boot - The Phone Info tab in QtADB should show the /data partition's size while installing (would change between the actual NAND userdata's partition size and the EXT partition's size, will start installing content when it is showing EXT partition's size) and booting into Android.

A short note on my phone's configuration -

My idea of using the DataOnEXT Native Mount mod is to bring our devices (EU or TMoUS) as close as possible to a native Android device. In most native devices, the requirement of modifying the /system or /data partition sizes for every ROM or update does not exist. In fact you hardly have to get into the boot loader. Similarly, after this mod, my phone's configuration looks like this:

(I have two TMoUS HD2 - this is the config of the phone running TBD_SUNDAWG_V15_Lite_Edition_Themed)

Bootloader: cLK 1.5.1.0

Partitions and sizes: recovery - 10MB, boot - 10MB, system - 500MB, userdata - <whatever!>, cache - 2 MB, Misc - 1 MB (If you want to follow my example, EU users can do with ~400 MB /system). I try various ROMs and configurations in this phone, and have not touched the partition sizes ever since I got the DataOnEXT Native Mount working!!

Recovery - CWM Based Touch Recovery B8 by @munjeni

SD Card - Sandisk 16GB Class 2 that came with the phone, with 2 GB of EXT4 partition (created in Ubuntu). A faster card will give better results, but this ROM is pretty smooth even in this setup

That's it, thanks for reading - let's see how good/ bad/ ugly this mod turns out to be :)