There's no way to force a player to stay dead, your best option here is to roleplay. Missions in the map screen are in order just like you would get in the Commander mode, but all unlocked.
However: any items you want to unlock (tattoos, watches, clothing, or evidence items) will be able to be unlocked in both cooperative and commander. So you can basically 100% the game with friends (minus one or two things). :)