I am fairly certain that was Thomas Lennon. I was getting ready for the day while I was watching this morning and wasn't paying complete attention, and wondered if that was the real guy as well (since I've never watched it. I thought it was weird he would be able to communicate if he was in fact in jail), but when the guy started to sing, I was like "that sounds exactly like Thomas Lennon", so that's my final answer.
I didn't see your post until after I posted--but it's so funny that it's the singing that did it for me too. Up until then I was unsure then, bam, nope, that's Thomas Lennon!
Edit: My bad! I read your post and immediately commented and forgot to read other posts first so it seems this was asked and answered! But I'll leave it up anyway because I have weaponized narcissism (seriously, that guy was very interesting).