Easy,
1. Show the black flag (already in GP2,GP3)
2. Lit up the "pitcrew" light (already in GP2,GP3)
3. Lock it (easy, disable the ENTER/ Pitcrew key)
4. When car comes in pits take it out of race.
5. Show Retired with reason (already in GP2,GP3)
6. Switch to 1st Pos driver with camera view (already in GP2,GP3)
Done.
Morbid need I continue? Can you see how easy it is to have these functionalities?