Well the same way Sir Zeliek of the four horsemen did it.
Sir Zeliek was one of the Four Horsemen of Naxxramas. He was a paladin in life, so strong in his faith, that even in undeath the power of the Light still heeded his call, smiting his foes in battle.
Giving that he wasn't even infused with the light just using it, a lightforged draenei makes more than enough sense to me.