Is the 9 tooth a driver off a bmx hub or is it a cog off of a multi speed free hub cassette? If its off of a cassette, you can either lace that hub up to the rim you have on the bike now or if the cassette is already built up you can just put that on the bike. It will no longer be a fixed gear, but a singlespeed. I think it would look kinda cool if you could pull it off.