Yes, stick to your guns! Go with it, if he's got the skills, otherwise he will get confused, start losing the skills, lose confidence in himself and it will take even longer. I have seen it happen a lot of times.

Don't be stressed if he only wants to poo in a nappy. He won't be doing it forever. Think about your own poo anxiety - I hate pooing at work, some people won't do it at other people's houses, etc. So poo anxiety is a natural and normal thing. Happens to boys AND girls.

If you have a reward chart system happening, it can really help. Stick with things like 5 smiley faces = 1 new book/freddo/trip to the playground/whatever, rather than a treat every time he does something.

Good luck!