If someone knows that they are going to miss a turn, I think it would be a great idea if you were able to put in conditional moves depending on what the map looks like which will automatically happen once it comes to the your turn.
example: "IF" I had N Afr deploy 3 armies there and attack Brazil going down to 2 armies if i lose and advance all armies if i win, or if I no longer had N Afr do another conditional move.
It would have to be kept very simple, but it would solve a lot of problems in doubles and triples when their partners end up losing because of players missing turns, and will obviously speed up games.