> How important is it that this work with Reportlab 2.7?

It is not important. You are submitting pull request and the functionality you implement is up to you.

If reportlab 2.7 is not working then please make a comment in the code about that. That it does not work with 2.7 and works with 3.0.

> RuntimeWarning: Parent module 'PyInstaller.hooks.hook-reportlab.pdfbase' not found while handling absolute import

This just means that There are not files (even empty) 'hook-reportlab', 'hook-reportlab.pdfbase'.

Somehow pyinstaller is looking for them. PyInstaller should work fine without them.