Switch DPI's as part of ATI Display Scheme?

[james2008]

When I'm at my desk, I use a 21" widescreen monitor. I need a 120 DPI for things to be readable.

That DPI setting is too high when using the laptop screen alone.

Is there some way to automatically switch DPI's when an external display is attached?

I use the ATI "display scheme" tool to toggle between resolutions. If there's a DPI setting in the display scheme tool, that would be ideal. I haven't seen it though.