You've got to decide if it is more important to shut down and rest for a while, or try to add MPH for the showcase in January.
You can't realistically do both.
In order to add velocity, you need to strengthen muscles and refine mechanics. It's hard to do that without throwing. It's even harder to work on control and secondary pitches...
Comit to resting or preparing - whatever you think is the best course for your kid at this point. Just don't try to do both at the same time.
As for this particular showcase... No offense to PG or other organizations, but I would think January is the worst possible time to have a showcase.