Radeon: hot-swap VGA-out monitor

[Christopher Singley]

I have a Thinkpad R51 with an ATI Radeon 250 graphics card.  The card has a 
VGA out port, and I like to run in dual-head configuration (external monitor 
attached) using the MergedFB options of the Radeon X driver.

This generally works well; however I'd like to be able to hot-swap monitors & 
toggle at will between single-head & dual-head configuration.

Using the radeon driver's "MergedFBAuto" option works to allow X to autodetect 
single/dual-head configuration when it starts up.  If it starts up in 
dual-head mode, setting "MetaModes" like "1024x768-1024x768 1024x768" 
additionally allows me to use xrandr to dynamically switch back & forth 
between single/dual-head when I plug/unplug the external monitor.

However, if no external monitor is detected when X starts up, I don't know how 
to force a configuration so that when I subsequently plug in an external 
monitor, I can switch over to dual-head configuration on the fly without 
restarting X.

I imagine this must be a feature desired by many people other than just me.  
Can anyone give me a hint how to set this up?

Thanks,
cs