With ion detonators area upgrades fully upgraded, jump on top of a car or any other vehicle.

Shoot the ion detonator on one side of it (it doesn't really matter) and blow it up.

Putting more than one detonator may improve it, but it isn't necessary.

You may also want to go into the time warp thing, just so the car does not move (little easier to set them).

When they blow up, then the car will go into the air and carry you with it. I do not mean that you will ride on top of it, you will actually stick to it like glue.

If you position it just right, you can get to the top of the tallest skyscraper. It may just help while getting on top of some buildings, whether it's for fun or a mission.