Detect client sleep

[Proesmans Bert]

Hi guys, i'm experimenting with xbees implementing the zigbee protocol.
Currently i'm running asynchronous client code (with tornado) but i'm encountering the issue that commands are dropped when the client devices are in sleep mode.
How would i work around this given my Cyclic Sleep Period of 5 seconds?
I was thinking about implementing a command collector which also pings the client every 5 seconds before flushing its buffer to the device. The problem I see with this approach is that I cannot buffer command frames in between the library and the serial line because frame transmission is entirely abstracted by the library.