I agree that going to the next size screw would be a solid repair without too much trouble.
Towards the bottom of the thread below, you will find pictures of a repair that I made to my mag riser. I drilled and tapped the riser for a larger size aluminum screw that I epoxied and tightened into place. Once set, I countersunk it and tapped it back to the original screw size.
http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=14;t=006032 I chose that type of repair to maintain the factory screws since it was in an area that was visible. I don't believe that the factory screw in the aluminum is as strong as a bigger screw in the magnesium would be.
I have unsuccessfully tried epoxy thread repair kits on carburetors in the past and always end up using a heli-coil or the technique shown above.
Good luck and it's worth the effort, I love my mag handles.
Brad