Maybe they'd do a written debate at EvolutionFairytales. That forum is under absolute YEC control, and Percy is still a member in good standing there. Percy and Fred Williams also seem to get along well.
It also seems to me that at Fairytales they are actually more susceptible to reasoning than the person(s) running this QuestionEvolution blog.
A debate there could somehow also be preserved at evcforum.net.
That would be wise. They do not shy away from heavy "moderating" at Fairytales if things do not go their way.