Got a question here for my learned MSP friends.

My dad just beat cancer and is coming up to MSP to catch the OSU-UofM outdoor game with me Friday, part of a delayed birthday present. I'm an avgeek and FF because of him, so I want to take him up to the D observation deck when he gets in Friday. He's passed through MSP a number of times, but never made time to hit the deck.

I'm not flying that day, but would love to be able to get through security. My understanding is the best way to do that is to buy a refundable ticket, go through security and then cancel it. Wondered what the cancellation protocol was. Can I just do it online like I normally do with a cancellation, even after checking in? Also, any pitfalls I should be aware of?

Thanks folks for any advice you can offer.