Set up your console and controller so that it will not turn off automatically after a period of inactivity. Upgrade the
Sweep drone to the maximum and load up Level 49,
Super Sequence. Keep the X button pressed using a penny and some tape before you head to bed or work and let this method grind it out for you. I got roughly 1100 geoms every round (always made it past the blues, which is kind of amazing if you watch it). Make sure your controller is plugged in so it doesn't automatically shut off.
I finally made a video so you can get a better idea of what I'm talking about: