Mahagogo, we Canadians also seem to be deemed insufficiently immature to cope with real scores, and are only given percentiles. Here's my MacGyver method:

You can turn percentiles in scores using this:
http://faculty.pepperdine.edu/shimels/Courses/Files/ConvTable.pdf

And then add them up and convert to a GAI using this:
http://images.pearsonclinical.com/images/assets/WISC-IV/80720_WISCIV_Hr_r4.pdf

The only problem is you can't identify/ count any points over 19, so if you have scores that are listed as 99.9th, you can't know if they were exactly 19 points, or higher. So your GAI could be a floor rather than an final answer.

aeh - am I making sense? smile