Have you considered chunking some of the meat in his normal meals instead of grinding it all? I don't personally feed my cat any whole bones, as it just isn't feasible without either a dog getting to it or it making a bit of a mess. Instead, I simply cut meat into the largest size I think he will eat (about a square inch), and chewing on that does good things for the teeth as well. Particularly chewy meats, such as beef cheek or chicken gizzards are even better, especially if you can add a chunk to each meal.
Also, remember that simply feeding an all raw diet has the advantage of not having grains, which stick to the teeth much more readily than meat does. Even with a little canned topper, I'm sure his teeth will stay much cleaner!
If you can pair those once a week bone in meals with chunking his daily meals and weekly teeth brushing, I would guess his teeth would stay healthy for a very long time.
Another thought would be to remove some of the bone from his mix. In addition to constipation, too much bone causes problems with certain nutrient absorption. If you recalculated the mix to have, say, 5-7% bone instead of 10-15%, you could maybe feed 2 bone in meals a week. Chicken necks and wings are VERY high in bone, at 36% to 46%, and that is the numbers with skin included, so be cautious. You didn't mention if you make your own raw or buy a premade mix. Keep in mind that premade mixes are often about 15% bone instead of 10%, you would have to be even more cautious adding more bone in that case.
Lastly, my final thought would be to give him a bone that he couldn't actually eat, such as a beef rib bone. If he was interested, he could then chew (or at least tear the meat from the bone), without the possibility of him getting more bone than he needs. In the summer I like to throw my dogs outside with them, and then once they have been stripped of meat and dried out they make a nice chew toy for them inside.