I have a couple that I use. I placed them easiest to hardest.
Liberally smear anything spread-able over the entire interior of KONG (peanut butter, cheese whiz, cream cheese, liverwurst, last night's gravy), Stuff a layer of the dog's kibble, pack in hard, Drop in something delicious such as bacon, cheese, treat etc., Continue layering kibble/treat/kibble/treat/etc until you fill KONG to top. Use your knife to pack in HARD! Wedge two medium-size Milkbones into the large hole at bottom (You might break a few at first but keep trying!) Turn KONG over and shake. If something falls out, pack in harder until you can shake it and nothing falls out.
Soak kibble in plain yogurt/beef broth/anything tasty and liquid until slightly soft. Follow the recipe above. Place in freezer overnight
Mix plain yogurt with plain oatmeal to a very stiff paste. Smear entire interior of KONG with something spreadable such as peanut butter. Place the tastiest thing you can at the small-end hole of KONG. Continue to stuff KONG with layers of oatmeal mixture interspersed with small treats until you get to the top. Plug large hole of KONG with two medium-size milkbones, making sure their ends are firmly stuck into the oatmeal mixture. Freeze hard and give to dog.
http://westwoodanimalhospital.com/BhvArticles/kong_stuffing.htm -At the bottom are some good recipes.
http://www.kongstuffing.com/?page_id=16 - Full of great kong stuffing recipes even ones specific for age and weightloss.