1. Obtain eggs. 2. Go to central Lumios, around the Eiffel tower gym. 3. Put a rubber band/coin/whatever around the circle pad so you're heading straight to the right/left. Because of the way the camera works there, you'll be constantly moving without leaving the area. 4. Get a sandwich or whatever. 5. Come back. You should see "oh." press A, let the Pokemon hatch, etc. etc. 6. Rinse. Repeat.
On 12/02/12 I said I wouldn't change this until something impossible happened. Now, Earthbound just got re-released in the US.