You could get him to witness the marriage certificate, I know it's not required, but I believe there is a space there available?
It's possible we're going to have 2 BM, and 2 MOH, we haven't got it completely worked out yet, but MOH1 - would stand next to me, and take my flowers and what not, and MOH2 will likely sign the certificate.
BM1 will stand next to DF, probably have the rings, BM2 will sign the register and say the BM speech.
BM1 will probably organise DF bucks night too, but that's nothing to do with the ceremony...