[sweetjazz]

I don't know the answer to your question, but I do think that your decision point is the turn here. You should either call the turn intending to showdown or fold the turn.

I'd usually call down in this situation if it was the BBs first donk, expecting to see 5x or 76 or some such, but expecting the combo of improving to the best hand on the river plus the possibility he's donking A3 or J9 or some such allowing me to win unimproved to make calling down turn a thin profit.