Hi K.,
What I'm going to suggest sounds awful .. . .but it's safe. :-) Have you ever seen kids on leashes ? they have these leashes that, I think, come with a chest harness, and that way your child can't run too far. It also prevents someone else from grabbing your kid and making off with him. I know it sounds a lot like walking the dog, but I've seen the on the ski slope to keep a young (say 4 - 5 yr old from flying down the mtn out of control; and in malls. If he has the option of sitting in the stroller, OR walking, with the tether, then he'll have some control, but you can also tell him it tethers Mom to him, so YOU don't get lost. My sister had a friend who did it that way, and said that Mom was on the leash. It sounded better to her, but it DID work. :-) Then, try to give him things to be looking for. Maybe if he's working harder with his eyes and mind on the walk, he won't be so quick to be using his feet !! (I never had boys, but I did have girls who would want to walk the stroller, so we'd bring it on walks (usually 1-2 miles in those days) and when the child got tired, the stroller got some use. The longer the walk, by the way, the more tired he'll get !! (if that's helpful to you ?? Like near bedtime ? hee hee
Good luck ! someday you'll see some other mom out walking with the exact same problem, and you'll look at your teenager, and start to laugh. and no one will know it's because you have an affinity with the unknown mom and are laughing at your old self -- not because you are laughing at her.