The potential for abuse exists, but I think this is doable. Checkmarks next to trusted teammates may be allowed, or even....oh, this is brilliant....
....You could have a list of "trusted allies" on your profile. If you are not around for a player-set ammount of time to take a turn, these trusted allies are alerted, and one of them may jump in to take your turn for you. Some of these "trusted allies" could be computer controls: "Kamikaze" would always attack, "Turtle" would always cautiously reinforce, "General Malaise" would play "normally", et cetera....