Easiest way too...?

[CKappa]

Take off the stupid Spoiler/Luggage Rack without causin any damage lol still tryin to get into my trunk havent been able to get a spare key from pontiac for my car yet but still when i can get into it its coming off

[dguy]

It's been a while, but...

The ribbed strips which sit on top & inside the rails can be pried out with a flat-bladed screwdriver.  You'll find fasteners concealed within.  There are also a few fasteners under the luggage rack's "wing" which allows you to separate it from the rails, but they're easier to deal with after the rails have been removed.

I think there are also some nuts which have to be removed from the underside of the decklid. 

Filling the holes & having the plugs last without shrinking or cracking is a bit of an art form. 

[FieroBUZZ]

Do yourself a favour and just find a decklid without the rack (and holes).  It is a major pain to fill them properly.  If you do, use SMC adhesive not fiberglass.

Yes, chances are they will crack down the line.