i saw a guy mod an old pair of molegrips that looked a lot like this https://www.google.co.uk/search?biw.....0.0.0....0.tziEFqWLDIk#imgrc=Q0X4F17y2qA-AM:
but instead of the bolt stcicking out the bottom it was a long bar with an adjustable height bottom jaw.
I made one of those for clamping stuff down on the drill table. I used a set of straight jaw vice grips - they are useless for anything else!