Correct me if I'm wrong but can't you just use the 3 point sling as a 2 point? You don't *need* to use the 3 point option however it's still there if you ever need it.
Heres a youtube video (note I don't know how good quality it is since I've never used a sling however this guy seems to know his stuff):
YouTube - Specter 3-Point Tactical Sling