Hi Peter,
Why don't you replace the screw with one of these;
2x Captive 1/4" 20 Tripod / Monopod / Quick Release (QR) Plate / Camera Screws | eBay

They have their own slot for most coins up to 50p (UK money) and should just be a straight swap!

The Milich and RRS grips are great, and the inspiration for building my own!
Hope this helps?