Are there any known solutions to manually or automatically expand a TrueCrypt volume on Mac OS?
This is possible if you have access to a win* box. Run
extcv (from http://extcv.sourceforge.net) which will resize the TrueCrypt volume. Then you can use
diskutil resizeVolume <vol_id> <size> on Mac OS to expand the filesystem.
This works great :) Here is a simple tutorial: