It seems to me that you are handling everything right. I would continue set up situations where you can manipulate the bully stick. Be prepared, if snaps don't let that stop you, reach in and get that stick without reservation. Walk up to him like its yours and you own it and want it back, use your feet to show him your boundaries. That will sometimes back them away from the object, then you can treat him right away. Or by moving forward, sometimes you will be able to put your foot on the edge of the stick and if he snaps he gets your shoe, no harm done then just inch your foot up the stick until he has relinquished it or isn't protesting and pick up the stick. Again, treat immediately. Don't talk to him when you are doing things like this, it will send mixed messages, it's pretty hard to reason with a dog. However if you keep doing the "hot dog switcheroo" you can talk to him then, and teach him the "drop it" command. When he is dropping the stick for the hot dog, say "drop it" and treat with the hot dog. He'll think it's a game and love the idea! Hope it helps!
