I completely understand why you need this, and we need to make sure such things work, so please don't give up getting it to work.
(you can email me at firstname.lastname@example.org
if i don't keep following up and making sure this will work).
I think you should be able to write simply like this in your alias results and search folders:
\Portable Apps\Open Office Portable\
or just add \ as a search directory
that really should work and refer to the root drive where FARR is running, BUT if that does not work, i can either:
1) make it work in the next version
2) add a new macro variable like %FARRDRIVE% which refers to the drive that farr is running from.
i think #1 would be preferable.