I understand that it's not politically viable. But I don't think that disqualifies it from a suggestion worth exploring. Politics can change, especially when the money starts running out.
Ack! I wish our political system were so flexible as to permit this sort of exploration!
It is within the power of a province to credit 100% of provincial taxes back, although I wouldn't want to try that if I was governing a "have not" province, especially if part of the deal was cutting essential services subsidized by transfer payments.