I have not heard about any specific specials for the Westin. However, if you go to
www.mywhistler.com and search around, you will usually find some pretty decent offers on hotels/condos.
Also, as for the Westin, you could always try asking whether the SPG50 award is available. Or try searching for the rates one day at a time. The Westin webpage will simply give you the rate for the most expensive night during your time there and apply it to all of the nights you are looking for.
For example, if you are looking for a room from Monday - Friday, and the rates for each day are:
M-$179
T-$289
W-$179
Th-$179
F-$179
then the website (and often a reservation agent) will tell you that the rate for the entire week is $289.