IDITSTEPBWTCTVTIAWTPACFAPB = "I do not intend to sell the entered photograph, but want to convey to viewers that I am willing to produce a copy for a prospective buyer." Other than that, I don't know.
All this really translates as is "unlimited edition"; something that is made to order instead of made in a limited run ahead of purchase. In this case, a simple price will suffice. People don't expect to walk out of a show with THE EXACT piece from off the wall. If he really feels that it is necessary, he can give instructions to the gallery not to sell the piece off the wall (though it is NOT necessary to state this, as it is a given, unless talking about "vintage" or "one-of-a-kind" prints).
A better route, IMO, would be that if he really thinks the piece might sell, make a limited edition of five prints, and give them to the gallery to keep stored in back. As a buyer, that would be a lot less cheesy and more valuable to me than an unlimited edition that is not printed until it is ordered, IMO.