Another dumb solution, but a solution none-the-less:
You could make a championship off just one race, and in there state
RaceLaps = n
Saves editing trk files, but does mean you have copy and edit a champ gdb. Of course you still don't get a nice slider saying 1 --> 1000 laps.
I'm not that thrilled about how the number of laps have been implemented either. It appears to me that the slider only acts on the numlaps contained within the trk file. Is that right N2LO?