I did this a few times already. Assuming you have your onwad boarding pass go thru connection security, then upstairs to the Wing. Breakfast/Shower, ask to store your luggage and the piece of paper. Walk to the closest security checkpoint. They want to see the onward BP, passport and the paper. Then you walk backwards thru the security checkpoint, go downstairs and pass thru immigration as normal.
Coming back you just go back in thru security/immigration again.

Very easy, no eyebrows raised.