The trouble with scernarios that allow Napoleon to move to a defensive posture is that he hardly ever chose to move to the strategic defensive. It just hasn't him.
The longest period that he spent on the strategic defensive was from 1809-1812 and arguably it was literally killing him!
Spain instead of Russia does make alot of sense except that it would be unlikely to be supported by Austrian and Prussian corps. It is also doubtful whether Napoleon could do anything more than chase Wellington back to Torres Vedras at which point a rebellion in Austria and/or Prussia or incidents in Poland with Russia may force him to come back to Central Europe.
Napoleon probably realised this - the throw of the dice in Russia was typical of the man. If it had come off then Russia becomes a client state much as Austria and Prussia were. Then a Spanish adventure is possible or more likely a second peace of Amiens-style armistice.
The PoD is stopping of the Russian invasion. The only way to do this is somehow Napoleon is attitude is less likely to attack. Thats why in OTL he did attack Russia.
But I am probably overestimating Napoleon's intelligence by suggesting that this was even a possibility. Given his character, intelligent defensive tactics are considerably less likely than bold, risky attacks.
An even more sensible path would be to simply "stop while you're ahead", consolidate his power and establish a lasting French hegemony in Western Europe despite the irritating fact that yes, people who don't like him do still have the temerity to exist—but it doesn't take a genius to know that he would never have done that.
Yes, he would have never done that in OTL. Thats why you need a POD like this which have a slight adjustment with Napoleon's character.