Haven't done it but it shouldn't be too difficult.
You can buy the bell for bench cappers seperately so would just be a case of mounting it in a spring type mechanism.
Have you got or had a good look at a bench capper to guide you ?
Someone made a benchcapper out of an old car jack (non-hydraulic) base, mast and handle all present, bell came out the handcapper he got with his starter kit, some fittings etc, voila! benchcapper for $5.
I vote with Batz. When a mate and I started brewing we did something very similar, put the hand capper bell on an old drill press. And guess what, about 1 in 4 bottles was seriously undergassed and a bit stale tasting. So we went and bought a super automica and havent had a leaky cap since.
I made my capper from a little flypress that was used to set press studs. I was able to fit a capper bell to it with a screw and I cut the anvil off and made a little locator for the bottle neck. It is fast, simple and seemingly idiotproof.
Warb, If you still have the drill chuck, it will be easy to screw the bell off your hand capper then mount a metal thread screw and nut to it and hold it in the chuck, making sure the top of the bell is hard up to the chuck jaws. Oh, and put a bit of ply or something on the drill platen to cushion the bottle.