Is it possible to use extended displays with DVI splitters?

The goal is to share a dual monitor setup between two windows machines, the primary one being windows 7 PRO x64. Dual boot is not an option, I need to use two physical tower PCs.

I have purchased a KVM switch that has a single DVI output port - two in for two machines in.
I have two monitors that are both DVI that I wish to use an extended desktop on.
Both machines have a single DVI port. I have attached splitters to these but all I get is a mirror image.

I keep reading that all you can do is mirror with a splitter, but at my old government job I had this same setup working with a DVI splitter (well two, one per machine) and a kvm switch, I just can't remember what brand the splitter was. Then again, it was with Windows Vista... so who knows.

hi if your graphic cards have 2 dvi outputs could use something like this. Amazon.com: StarTech 2 Port Dual DVI USB KVM Switch with Audio (SV231DVIDDU): Electronics

A splitter can only give mirroring.

Some business oriented machines have a port that looks like a DVI, but is actually a specialized port that feeds 2 DVI monitors via a 'splitter'. This 'splitter' can take the 2 signals from the socket and drive 2 screens in extend mode (IIRC some extra software may be needed). Maybe this is what the OP has seen in a work environment.

This is such a card
The business graphics solution to drive all your displays. | NVIDIA UK