My pigs won't eat their peppers either. You might want to try kiwi a couple of times per week (instead of other fruits). They are quite high in vitamin C and both of our piggies love it.
Ly reassured me here:
http://www.guineapigcages.com/forum/...ts-please.html that if my piggy (only one at the time) was eating a cup of varied fruits and veggies, he'd be getting enough vitamin C even without feeding any specifically "high vitamin C" foods.
Good luck! We keep offering peppers (mostly only when we buy them for the humans at this point) but they haven't gone for them yet (at least not more than a nibble).
I have tried feeding the peppers before the other veggies (while they still have hay and pellets in the cage) and that hasn't made a difference. I think you can't force it, so just give them a nice variety of other veggies and they'll be fine.