I can tolerate variation in the absolute frequency (say 112 +/- 12 or even a little more) as long as the on / off ratio is stable. I have flexibility in the resolution too - I've been targetting 11 (ish) ratio positions including 0%, 10%, 20%, ... 100%. I need full off and full on.

Polling TMR2 is an interesting idea I have not explored - I'll play with that for a bit and see where I get to. Thanks for a new lead!