I agree that Blue Bayou would be the best place if she is a Pirates fan. Tell him to call and make a priority seating and make sure to check in early to get a table by the water. Then just talk to the waitstaff and have them put the ring in the dessert or have a little treasure chest arranged and have them bring that out.
Another thought; my husband proposed to me in the elevator of Club 33 while we were on the Walk in Walts Footsteps tour and since the tour guide was already set up to take a picture of us I have pictures of the whole thing. Our guide even arranged for us to have a special congratulations dessert when we got to lunch at the end of the tour.