What about the bishop sacrifice on h2? (27... Bxh2). with the idea of a pin
28. Kxh2 Rc2 (pin of the bishop).
29. Rd1 Rd4
30. b5 Rd4xd2 (check)
31. Rd1xd2 Rc2xd2 (check)
32. Kg1 (or anything else) Rb2
(you cannot take the pawn (32.axb5, because of 33. ab5 Ra8 1-0)
33. b5xa6 Rb6
And here, it sounds like you 'll soon have two pawns more, and an easy-going victory.
I didn't check all possibilities, though...
EDIT: OUPS, I made a mistake in the position!!
sorry! Forget all this...
you can still check if the sacrifice of the bishop on h2 cannot lead (after 28... Rc6) to threats of a classical mate with two rooks on g and h files. I think he at least has to give back the bishop, and you won a pawn.