Modifying video modes

Is there any way, short of modifying xorg.conf, to change the available video modes? When I scan through the four modes configured for my monitor, I find there is one (768x576) that doesn't work with my monitor (IBM G541 flat screen, using IBM 9512 in SAX2). I would like to remove that mode, but I don't see any options for this in SAX2. tnx