I see that this is possible on a T520 apparently (Triple-head on a Lenovo T520), but I can't see anyone claiming it's possible on a T420.
I'm running 12.04 and have Bumbleebee installed and working fine but I can't get the display port monitor to display anything. The power light flicks on, but things only render on my VGA output monitor, and Ubuntu's display settings don't detect the third monitor.
I'm not concerned with power management, ie, am happy to leave set on discrete graphics in the BIOS if that helps.
Is this possible? Thanks.