Your other choice is go with one of the third party ski schools. Whistler allows other companies to work the mountain however if you want one of these instructors you have to call well in advance..
We had a great experience with Extremely Canadian.http://www.extremelycanadian.com
This group doesn't really advertise that they do private lessons one day at a time (I suspect because of an agreement with the resort) but they do take half day, full day and groups up to 5 or 6 provided the group is all around the same speed.
The 2 instructors we had were Kristy Amour and Joe Lammers. (I know Kristy is not on the "team list" but you can ask for her)
Also Eski suggested we check them out and it was a winner. They do get the same lift preference as whistler ski school and the prices are in line with the whistler ski school so if you are planning to take a private anyway, check them out.
Also check out ski rentals on line if you plan to rent.. Last season it came out to 85.00 USD for the whole week (6 days) if you book online at least 3 days in advanced. This was for the high performance package, so you have to bring your boots. You can swap your skis at about 8-9 locations on the hill as well as in the village (no limit to how many times) and you can request them tune them up or wax them if needed. They had most of the top skis available to ski on so it was a great way to demo a whole mess of skis.