Can't get WMI filter to work

Hey all,

My situation - We have 2 offices, and we user Terminal Servers.

My problem - Only one office should have desktop printers redirected, as the other now has centralised printing (stopping redirection is easier than uninstalling printers on all computers in that office).

My (not yet working) solution - A WMI filter to detect the IP address of the users local PC, and only apply the policy to the subnet for that office (all IPs are assigned via DHCP on a specified subnet).

So here is the WQL that I am using, but I'm guessing that it is wrong (using the 'root\CIMv2' namespace) -

Select * FROM Win32_IP4RouteTable WHERE Mask='255.255.255.0' AND Destination Like '192.168.3.%'

I use the Group Policy Modeling tool when creating/modifying GPOs, but for what ever reason, the filter is never detected, so I can't see what is going on.

Can anybody please give me some help as to what to do here?

Thanks.