Mamash, the “selling” wouldn’t work. That would still be Lifnei Iver. I can’t sell my pet to a non-Jew for real if I know that he will spay/neuter it.
Charlie, how in the world did you get that P’sak? It doesn’t make sense. If you did it yourself it’s a clear Lav and as far as I know the vast majority (if not all) the Poskim hold that Sirus is Assur for a Goy also.
Wolf, as I said earlier it’s a Machlokes Acharonim between the Dagul Mervavah and the Chasam Sofer as to whether Basar Neveilah Bechalav is Assur Behana’ah or not (no one mentions Treifah but I assume that it would be the same Machlokes).