I like your idea. The Yankees made a crap load of money just allowing companies to plaster their names throughout the ballpark, and were able to keep the ballpark's identity. The Mets should have done this also. For 200 million or so, Citi would have the rights to some clubs, prime advertising spots, and would be one of the Mets major sponsors, but not ballpark naming, logo designing, etc.
The Wilpons need to find their cojones and explain to Citi that they can have a little bit of something or they will have nothing. Take it or leave it.