Gonna double post here to bump the thread, and link to the demo:

http://www.freewebs.com/bluecube/files/UpgradeDemo.zip

After I read the post again, I see you wanted an ITEM to do this. Too bad, you get a map that's constantly on the screen.

This can be either: 1) Easily modified to be activated via item, or 2) left as is, or 3) I can do a MapItemDemo or something.