A method I thought would work well is to play co-op as Cleric, hopefully with a Resurrect+ buff, but if not just play normally for a while and hope for resurrect to be one of your first gained abilities. Then just follow behind the team and focus on resurrecting an AI teammate - they usually have a bad sense of self preservation.
But after a night of dealing with near constant disconnects, or almost empty lobbies with Lv60 try-hards who rush the AI gate and finish the match in 2 minutes, I used a second controller signed in as a guest.
It's the same method essentially, but instead of following someone and hoping they die 7 times before the game ends, just find a place away from the action in a damage-over-time area (ie. the pink poison swamps) and park the guest there. Then with your main stand somewhere safe nearby and spam resurrect.
Be aware to keep count though, as the achievement unlocks at the post match summary.