Set Brains to 6 then put all the AI at +5 handicap and put yours at -5. You now have one brain. It is actually possible to win. Just order a dropship if you ever wanna attack. Evacuate your only brain when you have enough money from defending your one site. This game mode is way more brutal and super fun because you gotta be really careful when attacking.

Found another exploit. If you evacuate a base when all the maps are done appearing, you will be able to just have all the AI attack the untaken site. then kill all 3 brains and evacuate, rinse, repeat...

Don't you need to have a brain at a location in order for it to be captured? Wouldn't that make it virtually impossible to win?

Not really, to win you have to be the player with the biggest quantities of brains or gold.

Getting into a site, conquering it, killing all your enemy brains as they come to attack you, evacuate if you want to attack another site when you get enough gold, repeat, and eventually your enemies should reach 0 brains and you win.