@jakemohnen
The key adjustments are in Core / Game Mode Details and Modifiers / AI. In the Game Mode Details, you need to select the total amount of players (both bot and human) in the Maximum Human Player selection. Let's use 40 for this example.
Now, select the number of players on both sides. .....we'll say 4 against 36. 4 on Team 1 and 36 on Team 2.
In Modifiers / AI, you would adjust the PVE AI Count to zero for Team 1 and 36 for Team 2. That should populate Team 2 with 36 bots and force the 4 human players to the Team 1 side. ....the opposite is true. Also select PvE AI in the AI Type box in that same section so that real players will not replace bots on the opposite side.
This should work although I normally test things like this first. I'm currently just working off memory and the Portal editor online. Hope this helps.