Not very helpful, but I just bought 2x multi packs of character normal pants (Thomas and Bob the Builder) so I could say 'you don't want to get Thomas wet now do you?' which was very effective. Also meant any horrendous accidents could just be thrown away...,
That way he didn't get confused between nappies and pants, and the one time I tried training pants the wee just escaped anyway... Yes I had to carry spare clothes (and socks and on one memorable occasion shoes as well) around with me but it was cheap and he trained in a week
Sorry to not be able to actually help though !