That's not going to happen. Obama is so far-left that I simply can't support him -- and I voted for Bill Clinton twice. (I also think Clinton should have been charged with perjury, but that's a different issue.)
The Left in this country will simply not be satisfied with a centrist, which McCain actually is (by American standards). His history of bipartisan legislation (McCain-Feingold, -Leiberman, -Kennedy, etc.) is irrelevant to a large, vocal horde.