Perhaps some sort of challenge/response that needs to be handled every now and then when the crew haven't made any inputs to anything for a while, and a wake up call if they don't respond?
Already done on some aircraft...if there's no pilot input to certain flight deck switchery then after X minutes you get a nice little message on the screens, along the lines of "pilot response"...if you don't respond it gets a bit noisy
..if you continue to fail to respond it gets really noisy
