Temporary Wake Mode

My application uses multiple nodes that usually send a small packet of data on some defined period.
However, there are instances when I need to send a large amount of data (say 1MB or so).
My question is, with the radios set up for cyclic sleep, is there a way to make them temporarily stay awake during the sleep period when there is extra data to send?
Ideally, there would be a setting that forces the radios to extend their awake time for x ms every time they receive data (but still maintain the original synchronization). If no data is received, they simply follow the cycle and go back to sleep.
I have tried to do this manually by broadcasting a message that tells my devices to switch off sleep mode, but it does not seem to be very reliable.
Any suggestions about a good way to do this or is there a chance a feature like this will be implemented in a future release?

Thank you.