I've never done it but if i had to I might try a screw eyelet and a nylon runner/sling. Make the lower cut of your wedge then screw the eyelet into the area where the finished wedge would be, girth hitch the runner into the eyelet and attach the other end to an appropriate anchor (a tool loop on your harness, a nearby branch or if its too big for that, your rigging line.) Then simply make your top cut to finish your wedge and watch it swing clear. Seems like it would work in theory at least and an eyelet and a tool to screw it in with wouldn't be as bad as bringing a handsaw up.