Nope that's it. If you can find the 40GB iAudio you can have FLAC, but still behind the Photo in size. You can go the modified route and get a NJB3 or the like and replace the HD with something bigger and maybe push things a bit (though you'll be using uncompressed so calculate file sizes accordingly), but for lossless right now the iPod holds the title.
Only other thing I'll say, is if your set on lossless because of audio quality, I'd test a bit to see if your DAP of choice (and its DAC) is really up to showing off a significant difference between 320 kbps LAME/Vorbis/AAC and FLAC/ALAC (and resulting disadvantages of space and battery hit). Or you could be like me (considering) and not want to have two copies of everything and so use lossless portably, because that's what you want at home. I've used both ALAC and 256 AAC on a 4G iPod (and A900, Etys & HD650 with SR71/SM), and although never really ABXed the difference, I never really felt/heard anything missing in the latter lossy when switching. Course everyones ears are different and you may already have done similar tests since you have a 20 GB model.