If one were to gently chide a grammar nazi for ending a sentence with a preposition, should one use a comma as in "…the preposition, with which the sentence was ended" or not as in "…the preposition with which the sentence was ended"?

You don't want what looks like a dependent clause just dangling there.

We're saying that it's a restrictive clause?

I am. But that's just me. Maybe, if you're not in a hurry, we should wait for others to weigh in.

I'm not in a hurry. I checked out the infamous 'Churchill' quote (for which there seems to be no evidence that he ever attually® said it) and there seems to be only one of the many variants that has a comma in it.

http://www.wsu.edu/~brians/errors/churchill.html

I was hoping to hear from Father Steve on this but he's been pretty mum lately.

A bit ironic, really - Father being mum.

However, on a more serious note, my grammar check (for what little it is worth ) accepts the sentence with or without a comma.
Personally, I prefer it without but I think it might depend a little upon exactly what the beginnig of the sentence said, and how long it took to say.
(i.e., is there a difference, from this point of view, between a simple and a complex sentence?)

If one were to gently chide a grammar nazi

Don't. It'll end in tears ;)

If one were to gently chide a grammar nazi ... Don't. It'll end in tears ;)

Or Kristallnacht.

Never in-fuehrer-ate a grammar nazi.

If a preposition is not that with which to end a sentence, then what is it for?