Note: By the time you get to this area you should have picked up two Forge Stones. Go to Forge and buy the Evil Eye Helmet, which gives you two Lifeforce instead of one for each collected. Go to the area where you need to recover the Green Hive. While making your way out with it, you will reach an area with two big opponents that shoot the blue beam gun. One will be roaming up top while the other stands next to a wheel to open the door next to him. In the same room is a floor plate that releases the gnomes behind a cage door. Release the gnomes and use them to help you kill the both of the blue beam gun opponents. After they are dead, return to the gnome cage and open it again. They will keep respawning. Try setting yourself near the top of the stairs going down while facing toward the cage. Then, send out your minions. While they are out hunting, set your controller to keep sending out minions. When not killing, they are collecting Lifeforce at double the rate due to the helmet.
After acquiring the green hive, return to Everlight fortress. Get at least ten reds and whatever minions of the other colors desired, then go to the center of the courtyard where you hear the gnomes. Place the reds at the bottom of the stairs facing the gnome's prison, then activate the switch to let them out. The gnomes will run out but will be scared of the reds and move back. About five or six gnomes will run out at a time. Allow the reds to scare them into the corner. After a while, when you think there are a reasonable amount of gnomes, send the rest of the horde up there to finish them off fast. Some might get past you--either let them go or track them down and end them. You will only receive reds, browns, and green life forces. If done correctly, you should have no problem with dispatching the 1,000 gnomes and will never have to worry about running low on your favorite color minions.