Far from ideal, but another work around is if you have the play and charge kit, you can plug the charging cable into the controller when you go afk. The controller won't turn off while its plugged in. Then when you come back just unplug and play.

Hopefully they address this issue at some point. I've read various threads about this issue and people have spoken highly about a logitech wireless controller (don't remember which model off hand) that will still work after the controller falls asleep. So it seems to be some issue with the Xbox controller specifically and not wireless controllers in general.