This works if you don't squirm too much -
It's also possible, though inelegant, to attach a common commercial QD swivel to the staple.
Attachment 41780
One can sometimes use the issue web sling single-point style. Form a loop at the unattached lower end, put your arm through after the obligatory half-twist, tighten it up, and adjust length at the upper end. Works best if the sling is fairly new and stiff - too floppy and the hooks won't hold well around upper arm.