They already tried peddling that theme at the debate. One of the Republican candidates said that it had been 80 years since a Supreme Court nominee was put forth by a lame duck president. Yet the moderator brought up the fact that Reagan nominated Anthony Kennedy in his final year in office.
Regardless, the precedent (as they call it) is irrelevant.
Also, it's not a precedent, it's just an accident. It so happens that since Oliver Wendell Holmes, only one Supreme Court Justice has died or retired in an election year, and that was Sherman Minton, who retired on
October 15, 1956, when it really was too late to do anything about it. I know this seems like a pretty wild coincidence, but check it out
here, tell me if I'm wrong. A string of statistical flukes which mean that a thing has never needed to be done for the last 80 years doesn't mean that now, when it does, we shouldn't do it.
(Also, goddammit, a "lame duck" is an elected official whose successor has been elected but not yet sworn in. Until Election Day, Obama not only has the powers of the Presidency, but a mandate to use them.)