You could weld it if there was an internal tubing used as a slug.
My 1.125" stearing tube is 1.02" internal, You could insert a 1" tubes braze, weld, even epoxy it in there (at least 3" overlap for that), and then just use 1" threadless stem on the extended tube. remember this needs to be the good stuff like 4130 aircraft tubing. You have to decide where to make this joint. One option would be inside the head tube and use 1.125 down and 1" headset parts, or you could do it so it transitions underneath any spacers above the headset.
I'm not sure why you would want to do this, both systems are fine as they are.