Smiley I thought the same thing till a couple of days ago till I changed tactic... since then I flew through them and got my Elite license.
I did the same run with each one. Pick them up wherever, travel to the mine (just after the dam) using boost when the combo time is running low, do all the jumps and billboards, then head down to the south bridge (they'll be a super jump outside the mine which leads you straight to it, do all the jumps on the bridge heading back into the city, then directly after the bridge there is a right which heads to another billboard, go through that and then you'll go directly over a super jump. By this point you'll have 20x+ multiplyer which will usually be more then 500,000 points and takes no more then 10 minutes each time.