A birds eye view.
Since 1-1/8" tubing inside 1-1/4" tubing leaves too much tolerance, I'd have to get a thicker tube, or get special tubing drawn, or modify this tube. I chose to cut the length of the tube down the middle holding a very straight line. concentrate, don't let that saw wonder. You also want to crank the tension up on the blade.
It took not just 1 but 2 cuts going down the length holding a 1/16" tolerance. Just use a hask saw with the most teeth per inch you can find, a lot of patience and concentration.