How about you just tear the foil off yourself, and then quickly watch yourself?
If you do this in some large store, I am quite sure no one will even 'catch' you.
When they do catch you just tell them the foil was teared off already, and act like a child not knowing there's a CD key inside
Imo, it can be much easier than that.
Step 1: Go to a supermarket, something big that should have a section with games etc.
Step 2: Be sure its open 24/7 and only go there between 12 am - 4 am when there shouldn't be anyone in the store.
Step 3: Buy groceries etc, also take a game or more, be sure that no one saw you.
Step 4: Continue strolling through-out the store.
Step 5: Reach a part in the back, or somewhere with no cameras.
Step 6: Rip DVD-cases, snip photo of Keys, and be sure to take the code out, or anything related to it as they can trace the code to your steam account after you put it in.
Step 7: Shove DVD-cases somewhere.
and by easier i mean there is a very slim chance of getting caught.