You can't sit his team every week. No one should get a free pass. Unfortunately some people probably already got a free pass so to speak, but you can't leave his lineup empty.
This happened in my league last year. When I realized he wasn't putting a lineup in anymore, I took over the team. I simply left his "best team" in there every week, and only made changes when a player had a bye, or if there was an injury. This way the team always had a full, legitimate lineup. Since he had McNabb, Alexander, and Portis, there was no decision for me to make, so there was no problems with people thinking I was being biased. He only had like 3 WR's left too, so I simply left that team in and only made necessary changes. This was the best solutiona I came up with.
And it actually was funny how it turned out. He had T Glenn as his 3rd WR, and he got hurt. So I had to pick up a WR so he would have a full lineup. I picked him up D Bennett, and he blew up at the end of the year, and this "ghost team" ended up making the playoffs. Since he also didn't pay, the money he won, which wasn't much since he lost in the 1st round, went towards what he owed.
Thats how I handled it.