If its your own airline, that's just silly. If another airline, why not buy the ticket, if it looks good within your cancelation window, cancel. Then just walk up and ask for a Jumpseat. There shouldn't be anything wrong with that.

Just make sure you are not "listed" as non rev or jumpseat at the same time you "own" a seat for that flight. But if you canceled your revenue reservation and walk up to the gate for a Jumpseat, I can't see anything wrong with that.