If you can locate a PCI graphics card, you could use that as long as you have the drivers. As far as I know, you can't use on-chip graphics as well as PCIe graphics.
Other than that, finding a graphics card with 2 GPUs and more than 2 DVI ports would work, as would the config of HDMI, DVI, DisplayPort, but you'd have to find the right monitors.
Not entirely true, here at work we have Dell OPTIPLEX 780 computers and have two monitors set up, one from the MB graphics and one from an add on video card. everything working fine. Maybe it's because we still have the antiquated Windows XP still installed.