It might be worth contacting Davidson directly to see if they can provide you with any assistance. Your ds is too young to apply to DYS for a half a year or so, but once he is you should still be able to use those IQ scores if you can also get achievement scores to match. (aside: does anyone know if DYS takes non-US kids?)
I'd also check with your state to see what IQ tests they are using to get those types of numbers. Would they be willing to consider the WPPSI as proof that he might fall into the EG/PG category and pay for the further testing on the tests that might net those types of numbers? As far as I know, there isn't extended scoring on the WPPSI where you can get #s like that. There is extended scoring on the WISC-IV where they can derive higher #s for kids who hit ceilings.
This link from Hoagies may be of some help to you as well:
http://www.hoagiesgifted.org/highly_profoundly.htm
