Probably not. The reason why the conversions have more capacity is that they are using the already made UMP or grease gun mags for higher capacity. These are built on a double stack mag design. The USC is built on a single stack design. Doubling your round count in single stack is going to make that magazine very long and mighty silly looking.
I suppose somebody could design an aftermarket that had a transition from double stack to the single stack mag well. But we are talking about some serious money/resources to design something that there is not a huge market for (hell, even HK cannot decide if they want to keep the thing in production/import).