There are certain techniques that can be tried in cases like these (such as the "stop-start technique") but I can't comment personally on their success rate. It might be worth doing some research on that and trying it if you haven't already. I don't know if a doctor can help in this particular case although if you aren't too shy it might be worth a shot there too. You can also get numbing condoms that are supposed to help with premature ejaculation but I don't know where you get those.

The only other things that come to mind are either taking her part way with another method first before you start intercourse, so that you might have more chance of finishing together or, as I understand it (again I have no personal experience here) but is it true that a man lasts longer the more times he orgasms in one session? I'm not going to pry into what activities you and your wife do beforehand (and to be frank I don't much want to know ) but perhaps if this is the case, you could try a little more foreplay?