Besides the RADEON drivers still not have this support.
the last drivers release today in ppa's for ubuntu with xorg1.13 and up.
Now, when using the xorg.conf and being specific with the radeon driver and pci device. The system boot well, didn't crash, didn't give error about link/atom bios crash. and i know the system can boot perfect. BUT i cant see the screen YET. If i type the password ( doing this in a blind way) everything load ( i can rear) But i cant See it. no error in xorg.log or dmesg.
A BIG STEP AHEAD