How would you punctuate this sentence?

If someone gives you a hard time about ending a sentence with a preposition, feel free to respond to the criticism, as Winston Churchill, according to unconfirmed legends did, his tongue firmly in cheek:

'This is just the sort of nonsense up with which I will not put.'

Or should I use dashes and parentheses?

If someone gives you a hard time about ending a sentence with a preposition, feel free to respond to the criticism—as Winston Churchill (according to unconfirmed legends did, his tongue firmly in cheek):

'This is just the sort of nonsense up with which I will not put.'

Solution 1:

Both variants are dead on arrival, as the did is not part of the parenthetical "according to unconfirmed legends did". The "according to unconfirmed legends" is a parenthetical alright, and so is "his tongue firmly in cheek"; but the did is the main verb and thus an indispensable part of the parent clause "as Winston Churchill did".

That being said, I would discard the sentence as a whole because Winston Churchill never said that. That's a misattribution no longer to be put up with. Not an unconfirmed legend, but a confirmed lie. No need to perpetuate it.

Solution 2:

Start by determining what parts of the sentence could be omitted — that is, parenthetic remarks (such as this one) — while still making sense:

If someone gives you a hard time about ending a sentence with a preposition, feel free to respond to the criticism as Winston Churchill [according to unconfirmed legends] did [his tongue firmly in cheek]:

'This is just the sort of nonsense up with which I will not put.'

If you have the choice, start by thinking about whether those parts should be included at all, if what you want is brevity and wit: then no added puncutation is needed at all.

If someone gives you a hard time about ending a sentence with a preposition, feel free to respond to the criticism as Winston Churchill did [...]

Of course, it may be important to note the fact that this is meant to be an unconfirmed legend: perhaps you should keep that. What punctuation you should use depends on how much emphasis you want to place on it:

(Incidental) If someone gives you a hard time about ending a sentence with a preposition, feel free to respond to the criticism as Winston Churchill (according to unconfirmed legends) did [...]

(Matter-of-fact) If someone gives you a hard time about ending a sentence with a preposition, feel free to respond to the criticism as Winston Churchill, according to unconfirmed legends, did [...]

(Emphatic) If someone gives you a hard time about ending a sentence with a preposition, feel free to respond to the criticism as Winston Churchill — according to unconfirmed legends — did [...]

If you really want to draw out the sentence, keeping all of the words intact, you have to find the right balance of emphasis between the parenthetic remarks according to what you intend. For instance

If someone gives you a hard time about ending a sentence with a preposition, feel free to respond to the criticism as Winston Churchill — according to unconfirmed legends — did, his tongue firmly in cheek: [...]

paints a picture of Winston Churchill as a man about whom there are apocryphal stories, and who also happened to have a sense of humour; whereas

If someone gives you a hard time about ending a sentence with a preposition, feel free to respond to the criticism as Winston Churchill, according to unconfirmed legends, did — his tongue firmly in cheek — [...]

puts strong emphasis on the fact that whether or not Winston said such a thing, this is something one probably would only say to be facetious.