Yes, In my collection of scrap I usually have the next smaller diameter
of tube. polish it with a little sand paper and chamfer the cut ends
then tap things together. Your method works, I have done it when nothing
else was available, but the lack of a uniform tight fit all the way
around could reduce the load capacity...but, a couple of extra rosette
welds can eliminate that possible weakness by locking things together so
well that a "loose" spot in the internal fit makes no difference.

Michael Horowitz wrote:

A splice by inner sleeve requires an inner tube with an OD just under
the ID of the original tubing.

I've been splitting the tube, removing a 5/16 lengthwise piece and
then squeezing the tubing in a vice, trying to keep it round. I'm
running a bead along the seam, then grinding it down. Finally, I chuck
it in my drillpress and file to fit.

Is there an easier /smarter way to do this? - MikeH