Putin's main concern after he quits politics is his personal safety, not rebuilding USSR. Nobody in Russia wants back into USSR, an attempt at rebuilding would be futile and suicidal.
As for "bribing" the countries to join CU - that is the whole point of CU, which implies deeper integration, lower trade barriers, lower prices for gas etc. If you don't want to be "bribed", it is simple - don't take the money (and don't blame corrupt politicians, as if there is any other kind). We may question the motives - some countries are natural fit for CU, like Belarus or, potentially, Ukraine. Some, like Armenia come cheap and are more for the show to create an image of successful regional integration. EU does the same thing - Greece is going to be the major headache for years to come, the role of countries like Bulgaria and Romania in EU is entirely unclear (does EU "bribe" them by transferring money to their budgets?). While having core European countries in a union makes perfect sense.
I hope you realize that Ukraine is never going to be an EU member, which makes the whole argument surreal.