It's hard enough to cheat using the best line a computer can spew out. In order to cheat using a second-best line that still wins, you would need someone on the other end feeding those moves. It's just too complex to try to cheat in a "subtle" manner. And if you only cheat for a few moves, you may improve your performance, but you won't beat too many players several levels above you. Kasparov once said that if he'd had help for only one move, he'd be much stronger. The thing is, it's impossible to know which one move would have made a difference beforehand.
For now, I think it's difficult enough to cheat, let alone be subtle about it.
Yah, I just bought one on ebay. Its the Ivanov-2.0, and it comes with a free install of Houdini.