The Democrats were able to block Bork, so it is possible for the opposition to sink a nominee. We were about 5 votes away from filibustering Kagan, 8 for Sotomayor, but couldn’t block Kagan because of the RINOs like Lugar, Graham, Snowe, Collins, etc.
There is also the possibility to pass laws which invalidate some Supreme Court rulings. Of course Constitutionally-based ones would require passing an amendment, but I’m not too sure how much liberal policy could be defended on a constitutional basis, since those arguments often come down in favor of more free speech.
But it’s true that the ability to appoint judges at all levels would be one of Obama’s powers that would be more difficult to hold in check.
If there wasn't going to be such a high number of SC replacements or if Obama wasn't so radical your strategy would have a lot of merit.
I don't trust Romney on judges, but he could be pressured, especially in his first term if he hopes to get any conservative support for re-election. Like Mae West said to Cary Grant, "You can be had." We would have leverage with Romney, but none with Obama.