Onyx Note: How can I remap the back button to wake up the device

Hi. I'm trying to remap the back button to wake up my Onyx Note and to do this I've edited the file rk29-keypad.kl in /system/usr/keylayout/ in this way:

key 139 MENU
key 102 HOME
key 114 VOLUME_DOWN
key 115 VOLUME_UP
key 116 POWER
key 143 WAKEUP
key 158 BACK WAKE_DROPPED
key 104 PAGE_UP
key 109 PAGE_DOWN

unfortunately mapping the back button in this way to WAKE does not seem to be effective. It seems that when the device sleeps the back button ist inactive.
Any ideas?