Isn't that exactly what Obama was referring to when he used the cliche?  His reprising McCain is what makes it perfect.  Anything else would have lacked the proper punch.  Observe:

You can put A1 on a hamburger, but that doesn't make it a steak.

You can put snails on a plate, but that doesn't make them escargot.

You can put bubbles in grape juice, but that doesn't make it champagne.

...Or, if those are too "high-brow"...

You can draw cleavage on Danica Patrick, but that doesn't make her Veronica Zemanova.

No matter what, the pig analogy is still the best, regardless of whether Obama was referring to Palin (doubtful, by the way, as the best possible pig-Palin analogy would go like this: "You can put lipstick AND GLASSES on a pig, but it's still a DUMB-LOOKING pig").