[CentOS] Centos 7, ATI card, 30" monitor

Well, I got my user back to being able to use his system, but I've still
got one issue: it's running on the VESA driver - there is *no* Catalyst
build for this monitor, for CentOS 7. From a lot of googling, nothing's
been done since the summer of '14 (lspci reports it as a FirePro V3900).

Any thoughts, or pointers, as to if/how I can get X - he's running KDE -
to see the full width of the monitor, not just about 4" less, or is that
not possible with the VESA driver?

      mark