Tell us about yourself!
If you can hold the goggle and magnets in place securely, you can surely build up the epoxy in layers even without the staples. Their main purpose is to stabilize everything during the glue job, less so for stability afterwards.
No. The staples and magnets are glued to the helmet. The visor has magnetic clips built-in that snap to the glued on magnets and hold the visor in place.
I looked into this, too, but I only found quality helmets with built-in visors/goggles for well over $100 or even $200. I don't trust those $30 Chinese knock-offs and I'm not at the point of investing that much money.
@mcarrington: Great idea, too. However, I suspect the curved (convex) shape of the manufactured goggles makes handling easier as they retain their shape when taking them on off temporarily. I suspect a cut piece of plastic snaps back to flat shape, making reattachment more difficult, especially while riding.