It's actually pretty easy to buy the ticket and cancel it. I have done it several times. The funny thing is it has never been for the purpose of just getting to the airside. But, that's what it turned out to be. One of the times I was in the Skyclub at MCO and got tired of the delay and decided not to go. I had bought my ticket a few hours before and the agent cancelled it at the desk. I've also cancelled by phone and gate agents after checking in and going through security.