I don't know what to tell you...
How brave are you? This is a last ditch effort (cactus growers, please chime in NOW!).
I have successfully rooted cactus pieces. It would require that you cut the bottom off and keep cutting until there was no brown. Coat the the whole thing with a fungicide. Let it sit.... For maybe 2 weeks. Then place it on a pot of cactus soil. Firm it down so contact is made between the soil and the plant (but no part of the plant is buried in the soil) and wait. No water, no touching, no nothing. I have gotten pieces to root (and lost some to rot) and it could be months before you see results.
The callus on the bottom is the important part. The cactus has to form a callus.
That's all I've got.
Daisy