I agree with all the suggestions above..
Praise him and wait as long as need till he does it outside.. so FIRST THING in the morning is the best to start,. cause he needs to go i figure..
Also when he does it inside.. Say NO and then pick him up and put him outside.. so he knows when he does something inside he need to do it outside and the treats are working great.. so he knows its a party when he does it outside !
Good luck,. and let us know if there is some progress...