Can't you lock down the internet then?

I don't know how IT savvy you are releative to him so its hard to know how much help that would be.

I assume the porn is on the internet?

a. Lock the internet down
b. Expose him to friends and family
c. Print up articles about how hurtful porn is and leave them all around the home

I can go on... He has no consequences here so he really is just going to keep doing it until you give him a reason NOT to do it.