Re-route the supermatters waste output to go into a burn chamber.
The red circle has an injector, the blue circle has a scrubber set to scrub everything but plasma and oxygen (NOT SIPHON)
The cooling loop is just a standard loop, build however you want it.
I added a T4 thermomachine for even more cooling.
This nets me 7-15 mW of electricity in about 10 minutes.