place ~32/64 zerglings at random in the area you want them to be in. There's no function to do this, just sort of scatter them around.
Give 0 zerglings owned by player 9 at location to player 10.
Center location 0 on zergling owned by player 9 at location.
Give all zergling owned by player 10 at location to player 9.
Generate your random 5 bit number. //optional. You can also just randomize switch, give units 5 times via binary countoffs.
Give random 5 bit number zerglings owned by player 9 at location to player 10. //you'll need binary countoffs here
Center location 1 on zergling owned by player 9 at location.
Give all zergling owned by player 10 at location to player 9.
Order all protoss observer at location 0 move to location 1.
Repeat this trigger set 32 times, with the starting value increasing by 1 every time, ie:
Give 1 zerglings owned by player 9 at location to player 10.
Center location 0 on zergling owned by player 9 at location.
Give all zergling owned by player 10 at location to player 9.
Generate your random 5 bit number.
Give random 5 bit number zerglings owned by player 9 at location to player 10.
Center location 1 on zergling owned by player 9 at location.
Give all zergling owned by player 10 at location to player 9.
Order all protoss observer at location 0 move to location 1.
Place the trigger under "All Players" but put a death count condition in each of the steps, so that they only happen once (this is why computer players are so useful). I'm a bit lost on how exactly to do this easily. On the first trigger run, if all players have exactly 0 DC, set DC to 1 for current player (don't preserve it). Have another trigger detect when a player has left, then set that player's DC to 0. The only way I know to detect when a person leaves is via a unique unit or detecting when a trigger doesn't run.
So the pre-triggers should looks like this:
All players have suffered exactly 0 deaths of DC
Set DC to 1 for current player
Player 1 command exactly 0 unit
Set DC to 0 for Player 1.
Player 2 command exactly 0 unit
Set DC to 0 for Player 2.
etc... up to player 5
Preserve isn't necessary on these 6 triggers, since they'll only fire when a person leaves or at the start of the game. Player 1 will never actually run any of the triggers except the first one at the start of the game, so you can theoretically check all players for the first trigger, then player 2-8 for the second, then 3-8 for the 3rd, etc... I only included 5 players because if only players 6,7,8 are left, and player 6 leaves, the game is over.
"Parliamentary inquiry, Mr. Chairman - do we have to call the Gentleman a gentleman if he's not one?"