You can get bone meal for your mixture. You should be able to find it at a pet store. If not, you can find it online http://www.arcatapet.com/item.cfm?cat=17177
That should be a little easier than crushing egg shells. Depending how your dog eats will depend on the risk of choking. Dogs choke on kibble too. My dog eats very very slow, so there is minimal risk of choking. A dog that gobbles it's food will be more prone to choking, no matter what it's eating. Raw bones are excellent for your dog. They clean their teeth and help dog breath. I hope hubby will come around. I do find it difficult to find a bones small enough to be 10% of my dogs meal. It's more like 50%. Good Luck and keep us posted on how she does!!