Help! I think we broke our dog :(

That title may have been a bit clickbaity, but we do really need help!

So our 2 year old dog has had a habit of putting everything in his mouth since we got him (at 6 months old). Socks and shoes being at the top of his list, along with pillows, blankets, and really anything soft and squishy.

As a result, we taught him "bring it here" and "drop it" very early on. He's VERY food-motivated & praise/attention-motivated, so a couple of treats and some over-the-top excited attention helped to make sure he would give it back to us every time.

Now, however, he has twisted all of that around in his head into "if I bring mommy or daddy a shoe (after I play with it for a bit), I get a treat!". So that's what he does. He'll run to the front hall, grab a shoe, toss it around a couple of times, then race upstairs and stare at us until we notice what he has in his mouth - and he wants a treat. Lately it's progressed to him dropping the shoe in my lap, then sitting down and staring at me - the exact behaviour we expect from him when playing fetch, working on tricks, or any number of other activities.

For the past few weeks, we've stopped giving him a treat when he brings us a shoe, but the behaviour hasn't stopped. It was funny at first, but not anymore.

He's a smart dog, so we give him lots of activities to do. We joke that if we had a different style of door handle in the house, he would be able to open doors - because he tries to open the round knobs, but just physically can't.

He does have destructive behaviours when left to his own devices for too long, but this doesn't strike me as one of those things. He gets regular/frequent walks. I practice tricks with him at least 3-4 times a day. We play fetch, tug-of-war, and lazer-chase daily. He learns a new trick at least every 2 weeks (I wish I was a joking with that timeline. His newest is that he has learned to make a grumble-purr sound when I tell him to "purr like a kitty cat" LOL).

He doesn't act neurotic/upset about the shoes like he does when he's going stir-crazy from boredom. It's a learned behaviour that we have inadvertently taught him. Short of hiding our shoes constantly (which will be forgotten), does anyone have any suggestions?