The more I think about it, the more I think that Medvedev basically got the best deal possible. He gets to be President of Russia, with whatever powers that entails, commander of the Armed Forces, practically the leader of the CIS, and no matter what he does, all he needs to do is write "Putin made me do it" in his memoirs in twenty years, and everyone (at least in the West) will exonerate him. He could paint the State Kremlin Palace lime green and just say, "Well, Putin thought it'd look nice".
It's like farting in a room while standing next to someone who's morbidly obese. He's been given a blank cheque. Some of the power, none of the responsibility.