I made a lockspinner using just a large rubber band attached to my tension wrench, after realizing that the mouse trap spring idea won't work for my kind of wrench. It is the kind with the short end of the L close to the door and perpendicular to it, and I drilled a hole in the handle (the long part of the L, parallel to the door) and stuck the rubber band through it, making a loop knot. I hold the wrench with one hand, with the index finger on the corner of the L so it can pivot around but stay in the keyway, and another finger holding the handle. Then I pull the band in the direction it needs to spin and release the finger on the wrench handle. It works! One thing to watch out for is that the wrench handle doesn't hit the door knob if picking a deadbolt above it, so it might have to be angled slightly to clear the knob. I may post a picture at some point if I get a digital camera.
-IC