You can’t share planeplotter’s mlat with FlightAware at all - the planeplotter terms of use prevent it.
In theory it should be possible for piaware to support feeding data direct from a SBS including the timing data needed for FlightAware’s mlat but the devil is in the details and I don’t have a SBS to test with so it would be a bit of a voyage of discovery. I can work through that with you via email if you like - it will take some experimentation.