For some strange reason, I can't seem to get this. I've tried it at the airport, the industrial park, and the swing set and every time i do get 5 or more rolls it doesn't give it to me

I too had problems getting that one. Then one day, I was driving the infernus at the airport and got it without even really trying. Not sure which ramp I hit but the one that you hit and jump over a part of a tower is good (one by the health pack (pack there on multiplayer, not sure bout single) just hit it not going full speed and you can clip the railing and do tons of flips.)