We found that when Riley seen the stuffed frozen kong , he would run into his crate as he knew it was the only time he really got it. i watched him go at it, oblivious to the fact we were going out the door, I think he worked at the kong for so long that he was shattered and fell asleep, not sure if he barked a bit , dont suppose you will ever know unless the neighbours say .
I dont put kibble in , as you say it would fall out too easy.
I bought fish4dogs salmon mousse, it comes in handy little pouches, I put a spoonfull of that in the kong, then some grated carrot, then another spoonfull of mousse , layering it. I freeze it and take it out about 30 mins before we go out, its still quite frozen but he licks and licks and manages to get most of it. Riley is VERY greedy though and VERY food orientated.
Henry is still very young, dont worry.