You wouldn't be able to move your petunia far enough! Think about it...how far can the pollinators fly? They don't stop at the perimeter of your yard!

If you are dedicated to collecting seed from your own plant, you will have to exclude your plant from all pollinators and do the pollen swapping yourself with a small brush or cotton swab. I've seen people build little 'cages' covered with tulle netting.

If you hate the idea of keeping the hummers (and others) away, you could simply take cuttings OR locate seeds elsewhere. They aren't difficult to find.