I am so grateful to own multiple dogs. I have been using one dog to show another dog a behavior. It's worked beautifully.
Mike has never been a dog that you can pick up, cuddle, rub all over, ruffle his fur, etc. He just doesn't like it, and I can respect that. However, I do expect my dogs to let me touch them anywhere to check for injuries, bites, or tangles. Since touching Mike's belly is an issue for him, rather than forcing it or even click/treating it, I decided to use another dog to show him what I want.
Enter Cosi. In the morning I ask Cosi to lie on his side while I do a belly check which then ends in a rub, a tickle, and a kiss on the forehead. Mike has been watching this because I've so obviously staged it in front of him. It's worked. I can now come to Mike, ask him "Where's your belly?" and he will lie down, slide onto his side, and lift a hind leg exposing his belly.
You have to know Mike to know what a huge leap of faith this is for him. I hold his trust dear and know his limits and don't encroach on them. Checking Mike's belly in the morning is one of the best gifts I've ever gotten. Not to mention the lick (kiss) from him when the belly check is done. "Thanks, Mom!" he says.