Frankly, I despise spawn camping on either side. My solution is to either mow them down with Heavy, or use Dead Ringer to get past them and then come back to stab. Worst case scenario, wait it out and use Ubercharge.
Actually, I had a similar situation earlier, where I used Pyro to toss them aside, ran away, and then ambushed them while they were focused on the rest of the team. Axtinguisher, of course :V