If you would love to know the answer to this question, chances are that you too find the placement of the power button a bit too awkward for the hand. You’re not without hope however, as XDA Recognized Developer flar2 has developed kernel module that aims to rid you of this problem.
Named Sweep2Sleep, the module allows you to swipe the navigation bar from left to right to put your phone to sleep, a much more comfortable position as opposed to stretching for the power button on the top of the device. The module comes as a custom recovery-flashable ZIP, and it should be compatible with any ROM with init.d support and BusyBox.
If you would like to find out more, be sure to check out the original thread for more information.