As an addendum – if you were thinking of using a new-frame handler in a SyphonClient to achieve this, you shouldn’t make any assumptions about the thread the new-frame handler will be invoked on – assume it could be invoked on any thread, and that invocations for the same SyphonClient may happen on different threads.
As vade says, you can use QCRenderers on background threads, so long as each renderer doesn’t cross threads.