I have a Dahon Boardwalk of similar design. I'm not quite sure what you mean it's too close to your crotch, but in order to preserve 'foldability' you don't want to mount the bottle cage on the bars, stem or seat tube. I mounted my bottle-sized Air-Zound plenum on the underside of the top bar. I think you could also use hose clamps to mount a bottle holder further forward on the top tube.
To keep the bottle in reach you could use one of those behind-the-seat holders, but then the seat would not fold down all the way, but I have a saddle bag and it allows me to lower the seatpost almost all the way.
Maybe there is some sort of bottle handlebar holder with quick release that could be removed and repositioned when folded.
Good luck
