Doubt this will happen, but....
If they win tonight, maybe they start Peavy in six and save Lackey for seven. If they lose, keep it the way it is. Another possible option is Doubront in seven.
What I think happens is Lackey goes in six regardless of tonight. If they have won game five and Lackey gets into trouble early, pull him and put Workman, Dempster or Morales. In seven, they start Peavy and they have Doubront warming up at the slightest hint of early trouble. The point is don't let it get out of hand. Hopefully it get them through six, like last night.
Then they do the matchup thing the rest of the way. They would have: Tazawa, Breslow, Workman, Dempster in the seventh. They could even use Morales for a batter if htey had to. Lester would probably be available and maybe even Lackey, if he was pulled early. If they can make a move on Buchholz, then they would have Thornton.
My guess on the Cardinals end, they will stay with Wacha as long as they can in game six, but Wainwright will be vaiable for seven like Lester. Kelly will be on a short leash