1. Create a profile in profiles manager in Catalyst Control Center and save it
2. Edit the resultant XML file ...
Change
FanSpeedAlgorithm value
from
FanSpeedAlgorithm - Manual
FanSpeedPercentTarget_0 - desired speed from 0 to 100 percent.
Create a shortcut to CLI.exe with folowing parameters (it can be created automatically if you check "Desktop shortcut" in Profile manager):
"C:\Program Files (x86)\ATI Technologies\ATI.ACE\Core-Static\CLI.exe" Start Load profilename="Your profile name"
Put the shortcut into the startup folder.