At the risk of sounding like a broken record, I still like the set screw idea, and I've tweaked it a little.
Thread the screw through the bottom of the rail to where it sticks out, I dunno, 1/8"? Cut a slot for it into the handle, and stop the slot where you want the handle to stop. Forward stop accomplished.
On the other hand, if you were to use the asa hole (I cracked up typing that), keep the contour of the handle itself, and bolt a piece of cut-off handle there for the stop, and a return spring could even be mounted inside of that. It could still be nearly flush with the front of the rail, and look just like the handle.
asa hole