Smoke the kidneys for 1.5 hours at 250 F, or until they hit a temperature of 150F, then cool and refrigerate or freeze.
To serve the kidneys as a treat, I like to pull a frozen kidney from the freezer, let it thaw, then cut into 4 pieces (a convenient size your dog can easily eat).
Serve one piece as a treat, or supplement to a meal. The smoked kidneys will last for 3 days after thawing.