Ok, Then why dont you try establishing router in between Coordinator and End Device? This problem will be solved.
It's cheaper build a little circuit with (and, first of all, more powersave), for example, a microcontroller ATmega, in order to force hybernate mode, and wake up it, for example, every minute to check the coordinator avaibility. If coordinator is avaible, it can starts the comunication, otherwise it returns into hybernate mode.
What do you think about?