I was just thinking about this some more. You might need to slow this down.
One of the things you can try is to go to a park (or any wide open place) and let your wife approach from a distance. You'll probably see that the dog has two "zones", one zone in which he will be alert to the "threat" (ie. he will see her and stiffen up) and one zone where he goes off the deep end.
If you can identify the "stiff but alert" zone then you can play with that to desensitize him to your wife being in that zone. Use a command like "look" (or call his name) and reward him for every time he looks at you when your wife is in that zone. He should start to associate her being in that zone with something positive. Use lots of repetitions.
At some point you will probably find that his "stiff but alert" zone starts to shrink and your wife can get closer. Keep looking for that zone and shrink it with lots of rewards for remaining calm (or at least not going ballistic).
This will take time and a lot of repetitions but it's proven method for counter-conditioning.
Another variation on this is also worth a try. You will need 3 people. Start with two people the dog trusts and bring your wife into the picture in his "alert" zone. One person they stays with the dog and the other one walks to your wife while the person with the dog rewards for remaining calm. Wash/rinse/repeat.
The idea behind this is that you are "modeling" the behaviour you want from the dog and demonstrating that your wife is not a threat.
Once again, even an hour or two with a qualified trainer will help.