And that advice is worth exactly what you paid for it... Don't go asking for legal advice online anymore than you would ask for it in the barracks.
Scope mounts such as a Spuhr ISMS are viewed by DoS as ITAR restricted. Shipping to an APO/FPO/DPO, as gray as that area may be, is viewed by DoS as exporting. Try ordering one from TNVC, Optic's Planet, or other dealers to an APO and see what their take on it is. And I don't want to hear the "I did it all the time..." because people buy crack-cocaine all the time too, but that doesn't mean it's legal; they just haven't gotten caught yet.
http://pmddtc.state.gov/regulations_laws/documents/official_itar/ITAR_Part_121.pdf
http://www.exportlawblog.com/archives/2860
Get his US address to ship to if he wants it that bad, otherwise I would respectfully decline the sale. I hope with as old as this thread is that it isn't too late.
My background is several years of working overseas on DoS contracts, and requesting/ordering many parts and accessories for weapons that are ITAR restricted, including hundreds of scope mounts. This is for government owned property, and we still have to get the export licenses.