The easy way is to get some 5 minute epoxy and some release agent of some type.
For release agent, you can use about any kind of wax from Johnson's Paste Floor wax to paste shoe polish wax.
Use an old tooth brush to apply whatever release agent to the entire area of the grip frame, especially the grip positioning pin.
To be safe, you can do one grip at a time, so there's no chance of overflow gluing both grips in place.
Mix some epoxy and apply a small dab into the grip mounting hole. It doesn't take much.
Assemble the grips with the screw, move the grips into the best position to match the frame, tighten the screw, and allow the epoxy to set up.
Remove the grips, and clean up the release agent and the excess epoxy.