How would you react if the candidate gave you the answer I typically give in this situation? ("my current salary is irrelevant, here is how much I want")
I'd be fine with that. It's used as a discussion point to arrive at a salary the person is happy with. If your original salary isn't one you want to base it off, that's ok.
That's admirable. It's unfortunate that a majority of the money discussion folks in HR will end the conversation if a candidate doesn't give a current salary.