I’ll settle for Brit Hume. With his credentials, the establishment would be hard-pressed to say no to him.
Chris Wallace would probably do a good job as well--a bit on the liberal side but I think he would treat both candidates fairly. Major Garrett would be another one.
Bill Bennett. The man's an elite-educated polymath and mandarin-in-good-standing, they can't tell him "no, you're not good enough".
Bennett would make Barky lose his water, just sitting there looking at him. If Barky tried anything like the last debate, Bennett would gently pull Barky's testicles out through his windpipe. With the greatest respect and deference for the office, of course.