I think the best way to take advantage of the retributive aura would be to become a demon yourself. Either as an Outsider (Aasimar, Tiefling, that FR elf that can take a feat to be an Outsider, whatever) with polymorph to change into a devil, or as a non-Outsider using shapechange.

From there, you just need to figure out a way to do some ridiculous amount of damage in one turn. An Ubercharger could work, I guess, or maybe a Cindy-style blaster. Either way, that'd be the way I went.