tie on the lower one as you regularly would if using one hook, for the mid line hook i usually tie it on as i would on a tandem hootchie rig using single hooks with an offset eye. the line will remain flat on the shank and hook will keep straight. when doing it this way i usually do quite a few more turns around the shank of the treble than i would with the single hook.
the second , i tie using the method of attatching the second hook in the following video. i dont do the first as it is a little trickier on hooks without the offset eyes but still works.
http://www.youtube.com/watch?v=rNJx6dGUFr0