What kind of treats are you using? He may just not like those treats, or like them enough to work at them to get them out.

To try to entice him to eat them (and to use them up so they don't go to waste) try putting a little peanut butter, cream cheese, cottage cheese, yougurt, soft cheese etc... around the treat & in the kong.

Give him a treat seperate, not in the king, see if he likes it?

In your case you want to fill the kong with something special, something he doesn't get often or something he REALLY loves, so unless you do not want to add anything more to kong I'd reccomend you get different treats, ones that he goes nuts over.

I fill mine with all sorts of things, leftovers are GREAT for kong fillers, heck sometimes I cook extra leftovers just for that purpose.