When I hear folks say this about the V.P. slot, I am reminded of Lyndon Johnson under J.F.K. Kennedy brought him on board to draw in Texas support. Once elected, Kennedy basically told Johnson to go pound sand.
Johnson was a very powerful political figure. I doubt one could be found today that would approach his clout. And still Johnson was relegated to lap dog status under Kennedy.
Now Johnson did take over after Kennedy, so you have that going for you. Absent that, I don’t think McCain listens to anyone except himself. So we’ll see how far ‘a good V.P.’ will get us. My guess is about one millimeter.
I agree that he probably wouldn't pay any attention to his VP, but I think at best he is a one term Pres. if elected. Right now I don't think he can win.