I've been tinkering with sling designs for a while and found that I liked a 2-point sling mounted to the rear of the receiver on a single point mount and the other end mounted to the rear of my railed forend. It also worked okay with the front end mounted to the front of the rail.
Set up like that you don't really need anything fancy, just a Burnsed loop or HK-style clip plate on the rear & a swivel/mount for the front. You could probably use your carry strap to make the sling, add a fastex buckle if you want a get out of it fast option.
Lancelot has a good method for switching to weak side shooting with the sling set up rear of receiver to rear of railed forend. Take your support side arm and bring it through the sling so it is now just around your neck & switch hands like you normally would with a single point. No need to mess around with sliding tri-glides or releasing a buckle to get more room in the sling to transition to weak side shooting.