You might want to work on building toy drive away from bigger distractions, then reintroduce them once he's more able to focus. Or if you can consistently make the toy more interesting than whatever else is going on, you should do ok.
Some might disagree, and I have doubts that it applies to all cases, but the disengaging and sniffing around supposedly can be somewhat of a stress relieving behavior. I didn't buy too much into it, but I have seen Bus do it when asked something that's hard for him, like doing less familiar obedience stuff with his BALL. Right. THERE! On the ground! beside him. He normally has very good focus, and maybe it's just the distraction level of having the toy so nearby and clearly accessible (which he does ok with usually), but occasionally he'll just randomly veer off, avoiding both his toy and me, and sniff intently somewhere, then he'll stroll back over a couple seconds later. Initially I was annoyed that he was blowing me off, but this is a dog who is normally right beside me when we walk in the same area, and it seems related to his stress level, so now I try to lower my criteria a bit when he starts getting distracted or frustrated and it hasn't happened recently.
So I would wonder if he's not maybe a bit too stressed or distracted to value the toy appropriately in those situations. That's not saying that you can't build drive to overcome those factors, but it's something to keep in mind to avoid overfacing him.
You might have good luck with using a flirtpole to get better range/action on the ball on rope idea. The ball isn't necessarily the best flirtpole lure, but if he's like my dogs, it's the preferred item for play, so I get around that by putting a ball to get their attention, and a fabric item (hide or fabric scrap, or stuffed or unstuffed toy) for them to grip and to give it more prey-like action. The stick allows for better maneuvering to let him almost catch it, then rip it away at the last second! Or to wrestle it out of his grasp if he just barely snags it and doesn't have a good grip and watch him double his efforts to catch it again. Then you can transfer that intensity to tug and other games.
Also, make sure he's winning the toy/play often enough (while training and doing drive building work) to keep him interested. Ideally he will be so enthralled with the game that even when you let him win, he'll immediately be shoving the toy back at you for more. Two tugs/toys is a good idea, as you can use one to get him off the other without conflict (Bus won't take the tug from my hand, so I always throw it, but same general thing).
Make sure you end the game/remove the toys before he loses interest. Better to have 2 minutes of intense play and leave him wanting more, than to spend 20 minutes trying to entice him while he halfheartedly plays here and there, then eventually loses interest completely. It's ok to try different stuff, but when you get him interested, use it briefly then shelve it for later. You can always present the toy again, and eventually you should be able to work up to longer play sessions.
