Another alternative is to fill the Kong with a portion of the dog's daily ration of kibble and use a teaspoon or so of peanut butter to seal the opening, then freeze. That's what we do in the shelter here and the dogs love it. Still maybe not the best choice for a daily treat unless the dog gets exercised a lot more, but better than using only peanut butter, at least.
For that matter, rotating between various fillings will keep the dog engaged with the toy longer and make it more intellectually valuable from day to day.