First of all - thank you for rescuing.
Perhaps his cockroach move is a result of figuring out there's a leash on him? Try walking with him with the leash on but not in your hand -- drag leash. So he can get used to it being there but not be the focus of your activity, you know? Treat him while he's wearing the leash so as to create a good association with it.
Where are your pics of Portly?! We live for such things here.