Wow, bless his heart, what a tough start in life.
I would try to entice the terrier in him. Both Gracie Ruth & Yogi like to stalk, pounce and 'kill' their toys and each other.
They will stalk a toy that is being slowly dragged in front of them. You can buy some inexpensive fleece, cut 3 thin'ish strips however long you want. Knot all 3 together at one end, start braiding them and knot at the other end, or knot just short of the end and leave a bit of a tail. Then much like you would play with a cat, dangle it in front of him, drag in on the floor, flip it around - all to get him to attack it. Play tug-of-war with it - be sure to let him "win" enough in the beginning so that he'll want to continue. I also play growl with G & Yogi and they both know we are playing when they hear me. Soft toys with squeakers in them also are great to get their attention and entice them to play.
I would also suggest that you be down on the floor, so that you are at his level when you play. DH is real good at doing this with our gang. He'll lie down and play growl and "smack talk"
and they climb and crawl all over him. They'll play King of the Hill on him, knocking each other off, mug his face with kisses and try to climb inside his shirt if they see an opening.
But it may be that your boy simply won't be one to play much with toys. If that's the case how about trying to teach him tricks? Clicker training is great to stimulate their minds.
And walks, walking is the best thing of all for them. It bonds you together, it's great exercise, it's stimulates their senses and it's just plain fun for them. Get a nice coat or sweater for the colder days. If the weather gets too bad to go outside, I take mine to pet friendly stores (Home Depot, Lowes, Petsmart/Petco, Feed Stores, Craft Stores, Office Supply stores, etc) and walk them around there so that they are still getting out and seeing/smelling different things. Just keep an eye on him so that he doesn't have any accidents and be sure to have stuff with you to clean up immediately if he does.
A bell on his collar will help to make him 'visible' to people at work, and ex-pen or playpen would help to keep him safe yet allow him room to move around.