I've got 2 staffs and one of them is the same with her Kong like your boy. She runs up to the top of the staircase and throws it down so stuff will fall out. So I have stopped putting treats in there and use something more sticky. For a little treat I smooth some peanut butter on the inside. For a long treat (this takes her about 45mins) I open a tin of tuna (tuna in spring water) and mix a bit of water in it. Then I stuff it inside the Kong and freeze it overnight. Frozen is also good in the summer time to cool them down.
I also hide treats around the house. Tiny little pieces all over the place in different levels of height too and they both love that. It's exhausting for a dog using its nose sniffing out loads of treats so they get stimulated in a different way.
If your pup is already good on behaviour why don't you train little fun things instead. Like speak, whisper, shake hands, roll over, sit up like a rabbit... the list is endless