You SHOULD be able to do that, but I'm not sure how Apple dictates that kind of stuff. I know on the first 3 launches of Iphones we activated them right in store, but we would run in to problems for people buying them as a gift. If I were you I would tell them that you're giving the phone as a gift and you need to activate it at a later date. Again, I'm not sure what their policy is on that, but I don't think it should be a problem.
Cool, I can only hope that is the case.