You can't.
The closest you can get is an escort with the enemy set to "rogue," which will make the escort hostile to the player after being rescued, but the guarding group is, well, rogue.
Eva Destruction AR/Fire/Munitions Blaster
Darkfire Avenger DM/SD/Body Scrapper
Arc ID#161629 Freaks, Geeks, and Men in Black
Arc ID#431270 Until the End of the World
...Two factions conversing with each other like in safeguard mission weapon deals? I can do this with a non-hostile "escort" or "rescue ally" group, but if i want both sides to be hostile to (just) the player, I can't get it to work. Making a boss with his guards being a different faction just has them all facing one way and sometimes spread out. And the "other faction" doesn't get any lines!
Anyway to make this work?
-STEELE =)
Allied to all sides so that no matter what, I'll come out on top!
Oh, and Crimson demands you play this arc-> Twisted Knives (MA Arc #397769)