Why folding bikes at all? You could get an S and S coupled bike instead and retain a full frame.
http://www.sandsmachine.com/
There's a Vanilla with it (
http://www.fixedgeargallery.com/2004/b/chen.htm), stickerguy has a Thylacine with it on the way and I was looking at a Co-Motion one yesterday. They are truly beautiful.