This is the stem that comes with the downtubes. I think it is called an UNO adjustable (I haven't seen the exact stem for sale lately), there are many stems that are very similar that should work the same way. The key is to find one that tightens on the side with a 5mm allen. Then you can replace that with a quick release and washer (for faster folding).

This stem would probably work very well also.

http://www.nashbar.com/profile.cfm?c...%20ATB%20Stems

I'd stick with the shorter sizes so you don't create too much leverage, file the portion of the stem off in the picture indicated below to get a more vertical position for folding, and don't forget you will need a 1 1/8 to 1 inch shim to fit the stem to the handlepost (available at any good bike shop).



I've got over 1000 miles so far on my curve, running this stem and it has been great. (I'm 5'11" and 175lbs).