Perhaps add an option to specify the number of ghost cars being used. Then divide the number of times any ghost car has crossed the line by the number of ghost cars used. Basically average the laps across all ghost cars and display that average for i.d.7 ghost car.
Example- 5 ghost cars used. Player completes one lap. Display shows one lap by player. Currently, if 5 ghost cars cross it displays 5 laps for i.d.7. Instead divide that by 5 ghost cars to display an average of 1 lap per ghost car. It doesn't matter which ghost cars cross. Any 5 ghost cars crossing makes 1 lap and that is displayed.
I borrowed this idea from Bruce Yingling's HSSRMS program for Carrera digital.