This can only be done online. Have the host start the race with only a single lap. 
As soon as the race starts, have the host go across the start/finish line and then 
quit the race and return to the lobby. As the race is still going on, have the host 
go to game setup screen, then go to "Laps" and set it to as high as possible. 
The other racers in the race will finish the single lap race. If done correctly, 
the racers that finish that single lap race will get paid for the laps that the 
host changed it to when they exit.