I went through this about two months ago, trying to figure it out.
I concluded that xgl truly was on the way out, and it was a waste of my time to fight that battle.
I think it might be possible, but it became a game of 'whack-a-mole', where as soon as I'd fix one issue, that would generate another issue somewhere else.
Also, that was two or three months ago, and xgl is quickly slipping completely out of the picture. You'd be locking yourself into a stale set of packages and preventing yourself from incorporating a wide range of other new developments.
I liked the speed of xgl, but it was a memory hog, and it didn't work seemlessly with everything. I was scanning through the xgl development cvs tree, and it appears to me that they quit actively developing this package about two or three years ago, and show no indications of picking it up again. People have been valiantly applying bandages to the package for that last year or so in order to extend it's life, but those efforts are tappering off.
I've developed the impression that xgl has turned into a kind of "Franken-package" with all the patches and fixes, and each release only works with a specific rev level of other packages, and the rev levels of the packages it works with no longer work with each other because those packages have moved along.
Anyhow, thats my 2 cents. If someone can show us how it's done, I might go back and give it another try.
Gigabyte GA-P35-DS3L - Intel(R) Core(TM)2 Duo CPU E6750@ 2.66GHz
nVidia GeForce 7600 GS
2 GB RAM