I "trick" my Zaurus into thinking applications are installed to internal memory by using symlinks.
Two ways to go. The first is to actually install to internal memory, then find the biggest files, move them to SD or CF card, then create a symlink from internal memory to the new location:
ln -s /new/path-to-file/YOURFILENAME /old/path/to/YOURFILE
The second way is harder, to unpack by hand on expansion card and create links to them from internal memory based on the paths shown when the ipk is unpacked. Example of this for a tiff viewer is at
http://sdjf.esmartdesign.com/ipks/tiff.htmlsdjf