The floppy emu should work fine as the IIgs uses the same IWM floppy controller as the Macintosh Plus and SE. He just needs to add support for mounting 2IMG format images, the standard used by Apple II emulators for 800k 3.5" disks.

http://apple2.org.za/gswv/a2zine/Docs/DiskImage_2MG_Info.txt

Recent implementations to follow for accessing 2IMG files

Ciderpress: http://sourceforge.net/projects/ciderpress/

Apple Commander: http://sourceforge.net/projects/applecommander/