I've never made any of the recipes from the Kong site, some don't look too healthy though (depending on the size of the kong and how much you'd need to fill it).
Also Emily doesn't like peanut butter. What I do is plug the hole with a cit of cheese, put kibble and frozen veggies in it, fill with water and freeze.

I've also never trusted those Kong Stuff'n things you can buy at the pet store. If you just read the ingredients.....*yuck* LOL