If you have an Automotive Paint supplier nearby they carry something called a magic eraser.

Yoh hook it into an electric drill and once you start the drill, put the eraser on the stripe.

Trust me this thing will take off those stripes in a heartbeat. It worked great on my Mom's Chxxx van.

And It won't hurt the underlying paint either. I believe Eastwood also carries them too.

Check their website: http://www.eastwoodco.com