Thanx fot his great idea!! Why didn't I think of this??! I still have a VGA TV Tuner laying around (for using a monitor as TV without the need for a PC) It has Composite in, VGA in (Voodoo passthrough!!) and a normal VGA out. It doubles all modes and lets me decide what mode the monitor works in when it recieves the signal (1024x768 in my case).
I've opened a thread in the hardware corner to check if this can be done through component in (seperated RGB/HV)