Absolute paths in various PortableApp.ini files

I know this probably goes against the grain, but I was wondering if there's a way to put an absolute path in the ini file used by various portable apps. I've tried this with 2 programs (Thunderbird & OpenOffice) and in both cases it seems that absolute paths are not honored.

For example, in OpenOfficePortable.ini I've tried every variation I can think of for this line:

SettingsDirectory=d:\OpenOffice\Settings

The above line causes open office portable to not start with the error "The user interface language cannot be determined", while inside the OpenOfficePortable directory it creates a new directory structure along the lines of .\OpenOfficePortable\d\OpenOffice\Settings\user...

If I change the above to a relative directory it works fine.

The rest of this is some background:
I'm trying to come up with a PortableApp structure where all executables are wrapped into a single ISO and the user data files are in a parallel directory structure. Since the executables are in the ISO, I can't use a relative directory so instead I'm using the "subst" command in my start-up batch to create another virtual drive letter for my user files - and so I'd love if I could get these .ini files to map to this other drive letter.

If anyone's interested I can elaborate on why I'm doing this (for one, it's a lot faster to copy a single ISO than thousands of small files onto flash drives) - right now I am able to get Firefox to run directly off an ISO mounted on a flash drive with settings stored in a parallel directory on the same flash drive (but I cheated and am directly using Firefox instead of Firefox-portable because of this problem).

Any tips appreciated.
Thanks