In your estate, go to the pond that you can fish from. You should see a little sewer like object that is connected to the pond. If you look to the right towards the stream, you should see one just like it. Jump onto this other one, and your controls will be reversed while you are on it: up is backward, and down is forward.

Much like the location in your estate, there is another area that reverses your controls in the Sellbot Factory. Go past the Gear Room, and through the door. There should be a Goon in front of you, and to your right should be a path leading to the Paint Mixer. Immediately when you go through the door at the end of the gear room, go right towards the bars separating you from the chasm. In a little area around there, your controls will be reversed.