BIG business could hold the key to extending the tram line to Sutton, by sponsoring the system.
Sutton's London Assembly member has asked the mayor to look at the idea, which could be compared to the funding Barclays provides for the City's "Boris Bikes".
Mr Johnson has made it clear that while he supports the £200 million plans to link Sutton and Wimbledon with a new Tramlink line, it is unlikely Transport for London will put up all the money.
He had indicated that the local authorities and businesses set to benefit from a new line are going to have to pay their fair share.
Steve O'Connell, Sutton and Croydon's assembly member, said he accepted the need for local financial support but believed that getting major corporations interested in a sponsorship deal could help spread the burden more evenly.
He said: "We have Barclays sponsoring the Boris Bikes scheme and the Emirates sponsorship of the cable car system over the Thames.
"I believe there could be other corporations who would be interested in sponsoring trams.
"They are looking for recognisable and popular brands for sponsorship and the trams running in Croydon have proved to be both.
"The mayor has agreed to the idea in principle and I think companies would be keen to be associated with Tramlink if approached.
"I am very happy with the idea of a branded tram system if it helps get the extensions up and running."
Mr O'Connell added: "This is not a way of letting the mayor off the hook but the money cannot all come from the public purse."
Sponsorship of a sort already exists in Croydon, where the council has draped its Love Croydon brand across a tram.
The concept has been welcomed by Ross Feeney, chief executive of Successful Sutton, the town centre's Business Improvement District.
He is one of the signatories of a letter sent to the mayor, outlining the economic benefits a tram extension to Sutton would bring and urging him to sanction the scheme.
Mr Feeney said: "It is a creative solution. There is no reason why individual tram stops or trams could not be sponsored, or even the project as a whole."