I like that these are all reversible/no drill solutions. I just found this though, and it looks effective, although it requires drilling and this high quality version requires welding as well. I imagine this could be done more simply with some square stock, sleeves and bolts with welding being (suggested) but technically optional.
I did a rough model of what I'm thinking; I'm not an engineer so feel free to shoot holes in it. My main concern is bearing loads from the bolt sleeves on both the torsion beam and the stiffener tube. Perhaps careful sizing and using washers instead of spacers could mitigate that.
To clarify, the assembly shown goes entirely within the torsion bar, with flange bolts/nuts on outside passing through the sleeves. Sleeves are intended to spread bearing load from the bolts and to center the stiffener in the torsion beam. I haven't been under my car to take measurements yet, so dimensions are approximate (for this model, I used 1.25 square tube with a 1/16 wall, and 5/8 sleeves over (1/2" bolts).