Well well well... DS just turned two years. After totally refusing to sit on his potty naked before he turned 2, tonight he did it, whilst reading a book (I have a few cute pictures to show it).
When I said "this is where the wee wee comes from", he started examining his little willy....
For the time being, I think I'll just continue encouraging him to sit on the potty and hopefully, we'll soon have some success (nothing came out tonight 
. Any other advice?