Need A Beach

I'm going on a mileage run to DUB from ORD and the return flight is two hours after I land in DUB. I've been to DUB before and normally the plane lands, you walk through and tell the immigration officer that you are there for either business or pleasure. Obviously this is going to be different. So here are a few quick bullet point questions:

1) Do I even have to go through immigration at DUB? Is there a rope I can duck under instead of going through immigration, since I just want to get over to the departure area for the flight back to ORD (which is probably the plane I just got off)?

2) If I do have to go through the immigration thing at DUB and he asks why I'm there, how do I explain the whole idea behind a mileage run? Do I simply say, "American offered me a lot of fringe benefits if I flew internationally this weekend?"

Any advice on how to handle the immigration folks, and exactly what to say, would be helpful. I would have done a search on this, but an international run is going to be new for me and I'm looking for specific answers about DUB. Thanks everybody.

Beach