As most of you know, Carlos Beltran has a no-trade clause, as well as a $10M salary that the Mets will probably want to unburden themselves of. The no-trade clause gives him a lot of power. If he prefers to come to SF, he can insist on that and the Mets do not have the power to force him to accept another deal. This would make it a lot more likely that we can get him instead of, for example, Boston.
I would like to suggest that fans going to the game bring signs and make him feel welcome and wanted. E.g.,
"We Love You Carlos!"
If he sees that this town has knowledgeable fans who are ready to embrace him it could tip the scales in our favor.
A few extra comments. If he is willing to go to Boston or a number of other contenders, that will likely lead to a bidding war which include prospects as well as covering his salary. That may likely lead to a market in which other teams are offering more than Sabean will likely give up. However you feel about that, that is the way it is. It may be a long shot, but if we can get an edge by getting Carlos on our side, i.e., wanting to play for the SF Giants, then paying the $8M left on his salary, and giving up some less important prospects or players, could win the day.