To do this you need 3 things and have to be in free play mode
1. a vehicle
2. a droid
3. the self destruct power brick

heres how you do it
0. turn on self destruct
1. press L or R until you get to a droid
2. press it one more time so you get to a human
3. get into a vehicle with the human
4. jump out and switch back to the same droid and press Y
5. you should explode and end up back in the vehicl as a droid