Take a can of your favorite moist dog food. Add one beaten egg and some type of filler to bind it together. I grind up about a cup of my dog's regular dry dog food in my coffee grinder, but a blender or food processor would work just as well or better. You could also use a cup of your favorite breakfast cereal (omit the raisins and sugar!), or even whole-wheat flour. Add enough of the filler to make a stiff batter. (This will vary depending on how wet the canned dog food is.) Press about a teaspoonful of the mixture into mini muffin tins or form them into the shape of your choice. If you make the batter thick enough you can roll it out and use a mini cookie cutter. Bake at 375 degrees for about 30 minutes. You can adjust the cooking time depending on whether you want the treats chewy or crunchy.
There's a lot of room to experiment with these treats to find the right taste and texture to fit you and your dogs' preference. And don't forget to leave a baggie full of the treats with your pet client's owners. And include your business card of course.