There's no good way to go about doing it without it possibly cracking but here are a couple of suggestions you might try before drilling and tapping it. I've used all 3 methods with good success on other problems similiar to yours (not on my bike though).
1. Use a screw with a sheet metal type thread.
2. Squirt some Loctite in the hole, then stick a thin strip of soft solder in the hole and then screw the screw in with Loctite applied to the threads.
3. Fill the hole with JB Weld and then drill and tap the JB Weld.
Current Ride (Purchased new in Oct. 84) - 1985 Honda ATC 250R w/ ESR 310cc big bore kit
Wife's Ride - 2009 Polaris RZR 800
Kid's Rides - 2009 Yamaha Raptor 700, 2008 Yamaha Raptor 250
Former Rides - 1975 Honda XR 75, 1979 Yamaha IT 175, 1978 Honda ATC 90, 1980 Honda ATC 110
got sand?