Opposite logical fallacy to "straw man"?
The straw man fallacy is where an attacker sets up a "straw man" that looks superficially similar to their opponent's position, but is more easily attacked. They then attack the straw man and claim to have successfully defeated the opponent's position.
In the reverse of this, a defender sets up an "iron man" (perhaps?) that looks superficially similar to their own position, but is more easily defended. They successfully defend the iron man and claim to have successfully defended their own position.
Is there an existing word for this latter fallacy?
I get the impression people often do it subconsciously, and sometimes before an attack is even made (examples). You could call it a straw man attack on behalf of the defendant I suppose (i.e. your straw man is your misrepresentation of the attacker's stance as an attack on the iron man) but that adds a level of indirection over the original situation that the fallacy describes. Also, if the defense is conceived of before an attack is made, the "straw man" wouldn't even exist yet - only a plan to construct him should the need arise - but the "iron man" is definitely there all along.
The Iron Man fallacy already exists (and, unfortunately, it has nothing to do with Tony Stark):
The iron man works like the straw man. ...[Y]ou invent an argument the person does not make all in order to make the argument the person makes appear to be stronger than it is. This has the related effect of making the critics look unfair, unhinged, or shrill. More importantly, it may serve to cover over the real vices of someone's position. (from TheNonSequitur website)
Unlike the straw man fallacy, the iron man fallacy is harder to strike down because of an emotional element that makes the critic look soulless. It is best used, perhaps, in heated topics like abortion and pollution, where attacks on one's position is tricky.
It is a form of begging the question.
Here is a good link that shows the difference between strawmanning, ironmanning and steelmanning: http://rationalwiki.org/wiki/Straw_man#Iron_manning
Another fallacy you might want to look into is the Motte-and-Bailey: http://rationalwiki.org/wiki/Motte_and_bailey