I too had exactly the same problem of lengthy T2 ring. It is too long for my Canon EOS M50 Mark II camera that has EF-M mount. Couldn't get a shorter T ring from local vendors. When I kept the camera without any lens close to the draw tube of telescope, I could use telescope focuser to get sharp focus. I badly needed a shorter T2 ring of width 10mm or less. Then I thought of extending focus of telescope using a Barlow lens that I already had. This is not the best solution but it worked (Now I see that you already considered the Barlow lens!) I could get good focus and take pictures of the Moon using the mirrorless camera. Here are pictures of my telescope with the camera and Barlow lens, and the picture of the Moon: