Multiple display help - any ideas?

I have a project I'm attempting and I'm not sure of the easiest way to go about this.

I have 1 computer for presentations running to 1 monitor.

There are 4 other monitors around it all attached to their own PC's.

I want to be able to - on demand - switch all of them to the feed coming from the presentation PC, then back to their own feeds on demand.

At first I thought the easiest way to do this would just be to run dual video out of the presentation PC, have one cable going to the static monitor, then run the other to a DVI video splitter. From there have 4 cables running to each of the monitors so that each monitor has their default connection (VGA) and the DVI connection, so that with the flick of the source button on each monitor they'd switch video. But, the monitors cant be reached, so thats not an option now.

Anyone have any ideas? is there a cool piece of hardware that I dont know about to do this, even in a few parts? A 1 button solution at the end would make it awesome... if possible.