Why?If you use it for steadying your hold,mounted on the pump tube, ,you may find accuracy broblems.The pump tube and barrel bend slightly with a charge in the gun,and flex when fired,a sling will affect that.Maybe a "ching sling" off the side of the stock?
For carying,I dont see the point,it's a very light gun,easy to carry one handed for hours if you dont have a big scope preventing a grip at the balance point.