I'm attempting this same thing and have managed to scrape up 13, but for the life of me can't get them consistently. I've heard going to campaign "The Three Towers" has 2 AI Titans that are free crits but its still taking way longer than it needs to, the hitboxes for those crits are just so dang weird.
I did it in about 4 hours playing Pilot Hunter. Lot's of players put their Titan on auto in this mode. Get to the high ground. Use amped Charged Rifle burn cards when you get them. Shoot at the red spots. Nothing more to it.
YOLO... It's like Carpe Diem for idiots. http://i.imgur.com/vrhzkRB.jpg