Allow option to put transitory RRD XML on root file system

On low memory systems this can be necessary if there are a few interfaces and thus a bit of RRD data. The XML files take up more space than the RRD. The space is only needed temporarily until the XML files are all packed into a tar.gz
This allows RRD data to save successfully on a low-memory where the limit of size of /var memory disk has been reached.
I also posted about this in the forum: https://forum.pfsense.org/index.php?topic=84693.0
This is a possible solution. I have tested it rebooting with the option on and off and the RRD data is saved and restored with both methods.
Feel free to comment about anything here;
Do you think it is worth having as an option for those on the edge of their memory limits?
Is this a reasonable way to implement it?...