I've been using the SpaceCitySpy strap that attaches to the trunk lid for about a year. It works fine, and no fingerprints. You do have to have a 'technique', though as too much muscle, and it'll pop back open, too little, and it won't close. Once I put my GT350 Track Pack Spoiler on, the additional weight helped it close much more easily.Try polishing it?
I wish Mustangs had a handle on the lid because I hate touching the black truck lid when it's dusty.
Good thing is I have that Califronia Special fake gas cap so I just grab that.