Well, I finally got the bit between my teeth and tried to work out how to properly support Dual Heads for my screensaver. After much struggling I stumbled on a solution that seems to work great. I can span both monitors, and select to use the main display only. But... When using the main display the second monitor fades to black, and then back to white. This has really pissed me off, and for the life of me I can't work out. The only GL_COLOR_BUFFER_BIT clearing I'm doing is with black, so God only knows why this sub view pops back to white.
I've googled but can't find much that seems useful...
I've been debugging this for about three hours now, as I have a feeling that the second monitor fading to white is about as useless as not having the option at all. On the plus side, it is running a hell of a lot faster on dual heads than it was. I doubt this will be good enough though... :-)