If his tendency is to put in all of his chips with most hands, you don't want to continue after the flop with hands that you are not willing to stack off with.
If you got the option: reseat to his left.
Don't go after him specifically. Don't call him down with 3rd pair or A high. Wait for a hand and take his stack.
If you're playing 10NL or higher, throw in a little session at 2NL, pick a nitty table and play über-lagg for a while just to try to understand what a LAGG player wants you to do. Remember: 40% of the time he will catch a pair. Just because he's playing every hand doesn't mean he never has anything.