I wanted to do something that wasn't too complicated and reused the 5bolt XTRs that came on the balfa, so I tried using the Salsa RingDinger plates. They're not as expensive as an entire new guide setup and can reuse the original boomerang that comes on the BB7s. Here's my setup:
Note these plates are more to keep the chain in place, they're not really meant as super strong bashguards, so keep in mind these would not be ideal if you hit the plates on rocks etc a lot
It's just a half assed solution and it works OK-
Oh almost forgot, you need 2 (identical) plates, one for the inside and one for the outside. Also make sure you have triple plate chainring bolts.