I've seen triple clamps welded in the past and considered it a possibility for this repair. Unfortunately, I have lost contact with two very talented weldors from my younger days. I'm sure they have long since retired.
I have used a couple of local guys for small welding projects, but their skills are more along the lines of structural steel and farm-implement repair. However, I recently met a gentleman who builds custom bicycle frames. He works in titanium, chromoly, and aluminum so I thought his welding skills would be up to the task (plus, he rode trials in the distant past).
This seemed like the most appealing option since I would get a reinforced part that was guaranteed to fit, and I would not have to deal with the bearing. Although I had been warned that aftermarket triple clamps use 7075 for the stem and 2024 for the clamp - both of which are essentially unweldable - I figured I would see what the weldor had to say. After an initial inspection, he agreed to do the job for $100.
I told him I had machine tools and could remove any excess weld metal, but I was concerned about distortion and made a slug that I felt might keep the bores from collapsing. He was free to use it or not at his discretion.
Upon further investigation, the weldor decided he did not want the liability. I completely understood but said I would not be using the cracked part and encouraged him to experiment, if for no other reason than to satisfy both of our curiosities.
Neither of us felt the result was satisfactory. No charge. I don't know if someone with different skills could have accomplished the feat, but it no longer matters. It's not a solution that would be generally applicable.