Last night a pinched nerve in my right arm woke me in the middle of the night. When that happens about the only thing that relieves the pain is to get up and sometimes a little use of the arm helps. OK Bubba enough back story cut to the chase.
With nothing better to do I made one to try. It works. I don't think it would replace a holdfast with a doe's foot on my bench but it works and I expect if the bench dog holes were placed with using a logarithmic spiral in mind it would work very well.
Here is a photo:
As you should be able to see, the arm from the pivot point gets progressive longer which pinches the work against a baton/stop as it is moved from right to left and releases as the work is moved left to right. Actually it is pretty slick and with correctly placed dog holes could work very well.