Here is a coupler that I have been investigating. This one is sized for 1 inch diameter on both sides, but other sizes are available
Item # C600E-187, Series C600 Keyless Rigid Coupling On Climax Metal Products Company
The coupler itself seems simple to install and uses a similar approach to cut-sleeve-weld. You'd cut, this coupler is the sleeve, then tighten the bolts (as far as I can see).
3200 foot-lb of torque seems beefy enough for my purposes - perhaps not for all projects.
The pricing (about $175 each) seems attractive enough to try it out. I just haven't gotten around to buying them and trying them yet.