We do already. How do you think those briefing sheets multiply into enough for all of the crew? The long-haul CSDs are usually half an hour preparing their briefing, working out allowances, etc. The point is its unpaid and therefore technically voluntary - not that the work would get done without it.
At least now the upgrade era is a thing of the past, the number of begging letters to be read is greatly reduced! Theres five minutes to spend with the Captain straight away!