How can I use a Linux box's display as a third display for my MacBook Pro? At work, I have a MacBook Pro that I use as my primary machine. I also have a RHEL6 box that has a dual-head graphics card. When my KVM is switched to the Mac, the second display that is hooked to the Linux box is not being used.

I know there is software the enable other computers to act as displays over a network without an additional physical display connection. Is there software that supports a Linux workstation being the third display for my Mac?
I'm not 100% sure if it'll meet your needs, but Synergy works very well as a software KVM and it supports any mix of OS X, Linux and Windows.