Wishbone: None that I know of. The levels are designed for two players, so they are impossible to complete alone.
It's great fun in co-op though. I highly recommend it. Maybe you can find someone here to play with? I'm game to give it a go at some point, but I don't have a lot of time available at the moment.
Edit:
Additionally, I recommend using voice chat when playing it in co-op. Additionally additionally, I recommend
not using the built-in voice chat feature, because for some stupid reason, that cuts out in the loading screens. Use Skype, Teamspeak, Mumble, etc. instead.
Thanks. I'll look around at work to see if anyone is interested. If not I might post here. As soon as I finish the single player and have free time that is.
sunshinecorp: If you're on Xbox I'm game.
No. PC.
Thank you, but not really what I'm looking for. I'd rather play it, or if all else fail watch a let's play video.