Just found the above item which will allows you to attach a QD sling to the OEM hand guard with no modifications to the gun.

Here's the link: QD Rotation Limited Sling MOUNT-N-SLOT

I just ordered it and will let you know how it works when I get it.

So why not use the loop attached to the gas block? The sling loop on the gas block is facing down. When you are carrying a gun in the front, you want the gun to sit sideways across your body and the loop at the front causes the gun to twist forward. Another issue is that you may have a need to remove the sling which you can't do if you use sling loops.