I have the Magpul M-LOK QD Sling Mount attached to the tube.
I used two #10 SS washers. I filed flats on them so that they would fit inside the slots. This centers the screw in the slot.
I used two 1/4" SS washers. I drilled out the hole so the football shaped part of the nut would fit inside the washer.
I took my pinky finger with the nut and 1/4" washer, slid it up inside the fore end. I then eased the #10 washer inside the slot and lined up with the other washer and nut.
Then I put the QD Sling Mount on top and eased the screw down through everything. I was able to get a needle nose pliers through one of the other slots to keep the nut from rotating.
It seems to work well.