You could drill through both pipes and put a screw with a nut on one end. use an aluminum spacer that you can buy at a hardware store or Home Depot etc. Just cut the spacer to the correct length to go between the inner and outer pipes. I like pop rivets for this they work well. You will have to stop squeezing the gun when the proper length is attained. then remove the gun/ pliers and cut the stem with side cutters.