I'm going through something similar that has been going on for months now. He was staying up till about 3:30 am for a while. Then he started napping around 10pm, waking at 1 or 2am and staying up till 5 or 6 in the morning, then waking at 1 or 2 in the afternoon. Now he's been staying up until 7am and waking around 5pm!!! It's just crazy. On top of that we've had a cold for over a month now - so I don't want to stress his already fragile immune system by forcing him to stay awake in the day on only a few hors of sleep. He's starting to get over the cold - so the time is coming for some major adjustments!
The weather should be getting warmer where I live soon and I will try to use that to my advantage. As soon as we get a warm stretch (I think it will be next week) I will begin taking him outside for a good part of the day. It stimulates him and the sun might help to reset his clock.
Tell me if you found any good solutions. Sometimes these things just fix themselves too.