I see 3 possibilities -
1. Tune down a whole step - ADGCFAD. It might take some work, but you would at least be in key.
2. Tune to drop A. All your riffs would probably start at the fifth fret, but it might be the easiest route.
3. Tune to a drop/double drop tuning. Tune to drop D, and then tune the B to either A, or to double drop, to G. I actually play my 7 in drop C, and I tune my 7th to drop F. It's more linear that way.
