I think the dabowhunter means a Heli-coil. I've used them in a kit form, available at most auto parts stores. They come in all sizes and allow you to maintain the original thread diameter so the original size fastener can be used. The kits have a tap, an expander tool and heli-coil inserts.

Now, I've not used them on archery gear, but have had good success with them in automotive applications, especially aluminum. I'd vote against boring a hole through your riser to add a nut to hold the bracket. The only other way, if the hole is that badly stripped, would be to drill and tap it to the next larger size. I'd use a drill press if you go this route, just to keep things running true.