I came across this discussion while searching the net how to remove this (plastic)decorative "button sticker" from the Home button of my phone that started to annoy me after only two days.
I did not want to apply any chemicals on my device.
I got a small needle with very sharp end, and gently pushed in the center of the round sticker, just enough to get some "leverage", and lifted, and voila!
I was surprised to see almost nothing on the back of the sticker but it seemed so impossible to remove ... guess the sphere-shaped sticker made it so.
Hope this helps.