A slice of lunch meat, cut into many small pieces
Make sure your dog is watching, and eat one of the pieces of lunch meat. Then throw a little of the meat to the dog. Continue to throw pieces of meat, until your dog is good and excited.
Throw the vitamin. Once your dog eats it, keep throwing meat, as if nothing unusual had happened.
If this trick doesn’t work the first time, try doing the same exercise a few times a week, without the vitamin, until your dog is conditioned to inhale anything you throw to it.
Please be careful not to overfeed your dog, or feed it anything that might not be good for it. Use treats and vitamins that go down easily, to reduce risk of choking.