The long bolts actually hold the side casing onto the engine casing, so the thread you stripped will not be accessible without taking the clutch side casing off, meaning removal of clutch, clutch basket, etc. This is a somewhat delicate job because there is a very large oil seal behind the clutch basket that makes it difficult to refit the side casing without damaging the oil seal. If you damage it, you'll have oil leaking into the clutch. Not good!
Helicoils and other similar products should work for this job but unless you're pretty handy with this sort of thing, I take it to someone more experienced. Remember, you'll have to drill out the thread in the engine case. Not a place to make a mistake!
Best of luck!
[Edited on 23-5-2003 by Felix]