My advice to you my friend is: first of all give Viagara a go (if you haven't already), try performing cunnilingus on your wife and whilst doing so, use the knuckle of your middle finger to massage her perineum ( that's the area between her pussy and her anus) as she is coming on your tongue, increase the pressure with your finger, also inserting your finger gently into her Anus sometimes works but only when she's close. Use a dildo during cunnilingus is another thing to try.
There are many ways to induce orgasm if you use a little imagination but if you really want your wife to cuckold you, then do nothing, she will find her own satisfaction and you may enjoy the lifestyle.
Good luck my friend.