yep, WMI filtering certainly works. The following WMI query will do as you require. Notice that you have to use ProductType = 1, this is because Windows Server 2008 R2 uses the same version. Also with service pack 1 the version changed slightly from 6.1.7600
to 6.1.7601, so the query will pick up both SP1 and non SP machines.
SELECT * FROM Win32_OperatingSystem WHERE Version LIKE '6.1.76%%' AND ProductType = '1'