Even with the pre-paids, they'd stil be able to see where a person with one of those is going and their shopping patterns, therefore giving them exactly what they're looking for. They're tracking the movement of dots to analyze shopping patterns. If a dot is prepaid it doesn't make it a "fake" dot. What would really confuse them (maybe?) is getting as many phones on your person as possible then running around in circles.

Why they would choose to attempt to discover patterns on black friday though is beyond me - consumer behavior on that day is completely wacky and inconsistent with any other day of the year.