Since Eliezer hasn't prepared by watching earlier debates then one solution could be to just use arguments from the theist's past debates in a simulated debate. As Eliezer prefers, he wouldn't prepare and would have to answer questions immediately.

There are two drawbacks: first it would just be "us" evaluating whether Eliezer performed well (but then, debate performance is always somewhat subjective) and we would lose the interaction of question, response and follow-up question.

Nevertheless, Eliezer's off-the-cuff responses to the theist's past questions could be informative.