J.K.
I wouldn't go to the effort to accommodate him on this one at all. He is 10 years old and definitely old enough to figure it out. I say be firm and be a mom. Take away his favorite priveledge, figure out what really means something to him. Does he play a sport or like video games. Find something big and stick to it. And definitely make him clean it up, every time! Suggest he lean forward when he goes too, that should rotate his body so that it points down if he's not willing to touch it. Any chance dad or big brother would actually sit and show him?
Having two boys myself, I know how lazy they can be. At 4 my one twin was potty trained and the other not, at least not to a point where I could trust him and it was simply because he was lazy and didn't care. So I had to figure out what he did care about. Turned out, it was his toys. And I offered him a choice, toys or diapers. He picked toys and didn't have another accident!
-J. (mom of 8 yr old twin boys and 6 yr old daughter)