Just use lightning to mix and join, consolidate, split, etc. Or maybe Liquid, although not sure exactly how that would work. Jeez. It really just takes 2 ln nodes you trust (or own). If you're paranoid, use your own hardware, erase all memory when you're done, and ditch the hardware.

I thought about writing up a guide on how to do this, but don't want the liability of publishing it, or the headache of dealing with people telling me how it won't work.