Mark,

   I haven't heard of an AOA being installed after closing the wing, but one possible way would be to cut an access panel on the underside of the wing where the lower pressure port would be located along with the seat for the drain tube from the upper wing port.  You could then reach and prepare the inside of the upper wing for its pressute port.  Then you could make a flange in the hole and put everything back together.

   The trickiest part could be routing the tubing from the two ports back into the plane.  Mine run through the conduit in the leading edge of my ES.  Like anything else, there's probably a way to skin that cat too.  I believe it'll be worth the effort.

   Skip Slater

   N540ES