According to the MX-Tech spring rate calculator, he should be fine with the stock springs if his full weight in riding gear is between 30 and 42 pounds. If he doesn't want to lose that much weight, maybe he could just buy some new fork springs that are the correct rate (stiffness) for his weight in full riding gear. He could swap them back out with the stock springs before he sells the bike, then sell the used, stiffer springs on e-Bay.
You will coil bind the stock springs with a preload spacer before you ever get them close to the correct rate, so don't even waste your time.
Beyond that, there are compression adjsuters on the bottom of the fork. Lightly turn them all the way in. Please don't crank on them as they reach the full in position. Light clicks are all it takes.
Raise the oil level to the maximum. Besides that, try a heavier oil such as 7.5 weight oil.
Canadian Dave, nice to see you on here again. I have test fit some 1995 and newer springs in 1993 - 1994 KDX200 forks. They will not fit.