No, I know how to make custom scenario's, but as you can see in the example I posted, there are set distruibutions where each player is given the territories designated, just by using a distribution mode.
In the example you can see it like this:
7 player (a)
7 player (b)
And no, I did make that game :P I always credit who I steal from, you know that!
Open the Distributions Window from the left side of your screen.
Click Add New Distribution on the bottom of the window.
Change the Type from Normal Distribution to Scenario Distribution.
Insert the name of the distribution mode (ex. North vs. South, 3v3)
In the box available, write the names of each of the distributions. (ex. North, South, Inside, Outside, etc.) Make sure that you put only one per line. These are what you see as (A),(B) on some screens.
Click Add Distribution.
Now, you can add territories to the distribution just as you add them to bonuses. Select the territory and check the box on the lower left.
To help you a bit more, remember that Normal Distribution means that ALL players choose from the territories selected. Scenario Distribution means that players must be assigned a distribution and can only choose from those territories.