Here is what I think you should do .....
Tell your boyfriend that you want to get him the new transmitter and you need him to help you pick it out.
Its as simple as that, if he wants to get it at the hobby shop take him there and buy it together or if he wants to get it mail order ask him to help you order it. This will avoid any chance of getting the wrong item. You then keep it and make him wait until his birthday to play with it.