You can use a WMI filter, but it's really ugly and unintuitive. There's no way to do this with Item-Level Targeting, as it only applies to Group Policy Preferences, which are a subset of configurable GPOs.
I always refer to this blog post when I need to do this instead of using Item-Level Targeting for some reason.
The WMI query that you'll be filtering on (from the blog linked to above) is:
Select * FROM Win32_IP4RouteTable
WHERE ((Mask='255.255.255.255' AND NextHop='127.0.0.1')
AND (Destination Like '10.0.0.%' OR Destination Like '10.0.1.%' OR Destination Like '10.0.2.%'))
In the example that you've provided, you probably want to use something like:
Select * FROM Win32_IP4RouteTable
WHERE ((Mask='255.255.255.255' AND NextHop='127.0.0.1')
AND (Destination Like '192.168.0.%'))