To do this, you need to turn the pedestrians follow you code on.

Other optional codes that you can use with this:
Pedestrians Riot
Pedestrians Have Weapons
Cars drive on water

To do this, you need to have a car that can do missions. (Cop car, taxi, ambulance, ect.)

Get in the car, and pedestrians will start getting in after you. When one is getting in, if you press the up button at the right moment, (pretty easy to do) the game will start to load and the pedestrian will be stuck to your car's side until you get out. If you turn on the cars drive on water code, the person will be stuck to the car while you're floating.

Note: This is a glitch, but it won't harm your game in any way.