Alpha transparency space in borders for stickers.

[Tetragram]

Hey Guys. I'm creating stickers, and I want to send to the printer, information that there's a couple of inches of transparency after the edge of the images. I'm making it about 2 to 4 pixels. Something small.

I have the cut out in Gimp, but can't figure out how to do that. 

I have read about the tools and searched the web as well but haven't found an answer. 

Any help is appreciated.