I really think automatic even/random deployment of armies during missed turns is the answer. When we used to play games of Risk during parties, people would stumble away from the board for (sometimes) hours. Before leaving, they would tell folks watching the game to take their turn for them:
"Dude, I own all of Australia and Madagascar -- if I'm not here to take my turn, just put one of my reinforcements on Madagascar and the rest on Indonesia."
It seemed to work pretty well sometimes.

I say let the game take charge of a delinquent player's reinforcements! If someone misses a turn, the game would go through the following steps:
(1) The game counts up all the territories owned by the turn-misser containing more than one army, then puts them on a
HOTSPOT list in order of descending number of armies (from most to least). If this would put less than
two territories on the
HOTSPOT list,
all territories are placed on the
HOTSPOT list.
(2) The game goes down the
HOTSPOT list from top to bottom, putting one of the delinquent player's new deployment armies on each one, starting back at the top of the list after reaching the end, until all have been placed.