challah yeast sourdough

I was planning to make Glezer's "my sourdough challah" tomorrow (for the first time), and had started refreshing my starter. It now turns out that I will have to be out of the house tomorrow, so must do my baking today. What I'd like to do is still use Glezer's starter (I've just made up the starter to be used in the final dough), and then add some yeast to the completed dough so it will rise faster, and so I can complete the challah today. What I was planning to do was add about 1/2 teaspoon of yeast to the final dough mixture. I figure then it won't need 6 hours to rise.