Eh?... From what I have seen mountain bikes don't really have stems, the frame goes right up to bar height...

I am going to have to study this. Or throw money at it. Probably both. There is a cool bike shop nearish me called Hashirin, they turn out a lot of custom dahons (click on dahon or tern in the side menu), just got to improve my Japanese enough to explain my crazy plans to them.

BTW did you try hairspray on your seatpost (if your clamp issue was slipping)? Works great. Mine was slipping and the bike shop threw in a control tech alloy seatpost as they said the carbon was wasn't able to be used as it would slip (it was actually a hassle getting them to leave the carbon one on). And it did slip till I used the hairspray.