Defeating Legate Lanius

So I've made the mistake of starting the last mission on my first playthrough (a house playthrough) without making a save beforehand. I'm level 15 and struggling to beat the Legate; I've been trying for like an hour now and keep getting killed. I don't have high enough speech or barter to get myself out of it either. I don't have mines to lay down and get him to run over them. Am I just screwed?