If you're using CSM, you should be able to solve that with GPx.
In GPx, go to GPxSet in the tabs at the top of the window, then to Session Settings at the bottom and instead of using the standard section, adjust the settings for each session. If you give them more fuel for one stint, there is a chance that they'll drive more laps. I've never tested this myself, though. Keep me updated, please, if it works.
GPGSL : Team Owner of 'Maverick Track Performance' (MTP)