Repairing Door Dings/Nicks on back bumper

[PeterNYC]

I live in NYC, which means i have the pleasure of paying an exorbidant fee to a garage so I can park our X3. What else do I get for this pleasure of over paying? Garage guys who bang the car around, though they claim to have "no idea" where all the dings come from.

At any rate, I know I can get an exact match on the paint from a the dealer, using the VIN....But has anybody done any touching up (or had the dealer do it)? The nicks along the door well seem easy enough to fix.

What i'm most concerned with is a couple of scrapes along the left rear bumper, which is plastic. There are two or three horizontal scratches (and, of course, some subtle yellow marks, the same color of the metal bars guarding the pillars in the underground garage).

I'm going to try to get the garage to pay for this, but I'm not sure how well that will work. Just curious as to the best way to go about such repairs, esp to the plastic bumpers.

I know it's all cosmetic, but it really bugs the hell out of me and every time I pick the car up from the garage my blood is boiling.