I've considered ways to record "encounters" with TSA as well.

Right now I think my approach would be to calmly pull out my phone, start the voice recording and then state the following:

"This is ------my name--------. It is xxx o'clock on --date--. I am at ---terminal / airport ---. With me are --- names of TSA and LEOs present ---.

Gentlemen do any of you object to a recording of this conversation in order to preserve an accurate record?"

If anyone objects I will cease recording but at least I will have them telling me not to record on record. If things go badly after that I would hope any impartial reviewer would have to question why one party wanted an accurate record kept and the other party didn't. Of course, that assumes that any reviewer would actually be impartial.