1 - Be in a vehicle as a Commander
2 - Go to Controls menu
3 - Go to Vehicle Movement
4 - Change the four movement direction as you like (example: IKJL)
5 - Go back in the game as a vehicle commander and issue movement orders to the driver.
You will be able to use movement orders only with WASD keys, even if you have changed them to IKJL
1 - Be in a vehicle as a Commander
2 - Go to Controls menu
3 - Go to Presets, select Empty, click Ok
4 - Change hotkeys for vehicle movements
Now, no matter what you use as hotkeys really. it won't work. Even if you choose the default hotkeys (WASD) they won't work anymore for issuing movement orders to the driver of the vehicle.