Unfortunately the answer is no. Gamma controls the entire screen brightness, and there is no way to set different gamma levels on different area's of the screen.
I have not used iGo8, but is there not a day and night setting right in the program?
EDIT: I just found this with a Google search, not too sure if it will help or not:
"Every device has it's own values for min and max brightness. Open your data.zip/config/devices folder and find settings for your device and rewrite them (the power section) to your sys.txt or set info names and device in sys.txt."