Not quite "strawman" -- a word for stating a non-believed proposition?

I would simply describe this as an extended version of the rhetorical device known as antithesis.

Antithesis establishes a clear, contrasting relationship between two ideas by joining them together or juxtaposing them, often in parallel structure.

Usually antithesis is restricted to clauses or phrases, but there is no reason why it may not be ascribed to sentences or even longer arguments.

Apophasis or paralipsis is a figure of speech of "affirmation by negation": discussing the negative qualities to emphasize the positive or even mentioning in passing that one is not discussing a subject (purely in order to bring it to mind).

Sorry to resurrect an old question but isn't this some derivative of playing devil's advocate?

In common parlance, a devil's advocate is someone who, given a certain argument, takes a position he or she does not necessarily agree with, just for the sake of argument. In taking such position, the individual taking on the devil's advocate role seeks to engage others in an argumentative discussion process.

It's not exactly that because that is a mechanism used to put your argument in sharp relief whereas you seem to de describing something that is merely opposite. Or perhaps I am wrong.