How about that squirrelflinger the clip of which was on the internet for a while --- I think it was a converted clay pigeon (skeet) trap - the springloaded arm that flings the clay into the sky to be shot.

Put bait (eg nuts) on the trap, and fix a waeight-triggered release (like a rat-trap).

Squirrel gets nut - squirrel gets flung away. A few tries and they would probably learn.