Here are some thinking-aloud ideas, hope one helps:

Cloth nappy training pants - that way they're pants and he feels wet but accidents aren't all over the outfit.

Let him pick 2-3 potties and have one in every room.

Can he take off popper nappy covers or just the velcro ones?

Can you just let him run around outside in just a T-shirt with a potty around for a few hours and praise him loads when he uses the potty (less floor-cleaning for you if he doesn't)? My MiL swears by this method of toilet training.