Can you stipulate that the husband can't revoke the tafweed talaaq?

No, you cannot.

This is a issue that goes back to general rules of contract.

And that is that the rights of contracts, especially with delegating others as agents, that the right to delegation is a permanently revocable act on the part of the principle in Islamic contract law.

Because otherwise it would be considered a permanent transfer of a right that that person does not have a vested interest or a permanent interest in.

And that would negate the objectives of having delegation to begin with.