Is there any way on a folding bike to put the rear derailler on top of the frame instead of on the bottom? I am looking at a 20" folding bike and the chains on most of the lower end models are dangerously close to the road. Any suggestions?

Is there any way on a folding bike to put the rear derailler on top of the frame instead of on the bottom?

No, that wouldn't work. The chain pulls along the top of both chain ring and sprocket, and the derailleur is down below to take up the slack. If you put the derailleur up top somewhere, pedalling would take up the slack from the top and put it down below, where it would cause havoc. Any suggestions? Internally geared hub.

Get an internal hub, no derailleur issues with them

Brian