any way to change the screen timeout when connected on usb and ac?

[ou2mame]

i need to have my phone on a long power off interval when connected to activesync and usb mass storage, but i find that if i forget to change the time back, i wake up, and my phone has probably had its screen on for the past hour or so because it received a text or something while i was asleep.

is there a way to have it turn off in like 30 seconds while charging on an ac charger, but stay on for an hour while connected to activesync?