Some guys are real defensive about their (for lack of better words) private life. Also, many guys who are into gurls with a little surprise
, feel that they have to validate their hetrosexuality (espically if they keep their interests a secret). Something you might do is send him a joke email, with a fully clothed t-girl and ask him if he would "do" her. If he says yes, send him a pic of the same girl showing her goods and see what he says.