Let's Bounce: I used the hard level Torment Fraud. Wait for a speeding vehicle to come along, most preferably a Minotaur Garbage Truck or a Taxi. Usually you can get some easy-to-hit speeders right at the start of the activity (as you're in a bonus zone.) When you see one, jump into it, but don't ragdoll. Just jump into it. The collision should give you enough momentum to indefinitely bounce around (even climb buildings if you smack between two.) You'll know if you have it, you can move around very easily. Then you wanna head towards the freeway and try getting bounced into the air and getting onto the freeway. Otherwise, you may also just go up the on-ramp but have plenty of height first if so.
Then just try to get it. You'll bounce a ton with this momentum going, so it's easier to try an plan your descents right onto vehicles. And avoid the garbage bags falling from Minotaurs. They cause a neat little glitch but can be an interference when you're going for the achievement. You can also try it on the regular streets, but you have buildings and random shit to dodge.