There are only two ways to use a blockchain-based currency in OT:

1. Trust an issuer to hold the coins, and then he issues the corresponding units inside OT. Markm's OT server is doing this now. This is the same as if he was holding gold, or dollars, etc.

2. Eliminate the issuer by putting the coins into a multi-sig voting pool. We are working on this now and should have the code ready soon. Note that this will only work with blockchains that support multi-sig.