Not sure if this will work on a EXO Glock but I have seen a few users on youtube have good luck polishing up stainless steel guns such as 1911's by using Flitz.
http://www.youtube.com/watch?v=RMQtbtXWKXc&feature=fvsr
http://www.youtube.com/watch?v=AlG1zFTkiWs
I thought the nickel boron (EXO) finish actually impregnated the metal, as opposed to being a surface finish?flitz is a great polish, but it is abrasive, so on a stainless gun it will polish it up to a mirror shine, but on a blue (or a exo finish glock) it will remove the finish leaving untreated metal showing leading to rust