The answer is clear: Someone has to play a traditional Lantern, build up to Ultimate Blackest Night, and then a bunch of non-Lantern characters can be issued temporary rings. GL Daredevil, Blue Lantern Spider-Gw--err, Woman (sorry, [@HenryJonesJr], reflex), Red Lantern Hulk...

EDIT: Blackest, not Darkest. I know comic stuff.