No way you can do it.
Not in that car.
To run clean laps is to run fast laps!
Plain and simple, the AI runs dirty laps and that equals slow.
My suggestion is to either run for your own satisfaction of getting great laps or if you insist on running close races, run a different car.
Trust me, no matter what you do it is nearly impossible to run close races with the AI.
UB57 created a race for NTSC users...
Enduros of 10-20 laps roughly.
Took the Nomad diablo then modified it to go from the stock 621hp to 549hp.
This put the pwr down to a point where we were constantly at a disadvantage of about 100-300hp compared to the JGTC cars we were running against.
Sure enough, most of us managed to whip the competition even with our bad tires, low HP and bad PWR.
So what's the point...?
If you want close races run with major under-dog cars.
If you want to run the S2000 LM concentrate on doing it perfectly and forget about those horrible drivers known as AI.
Of course, that's just my opinion.