In vCenter put all your local datastores in a folder, called 'LOCALS' (or something else you like) - this folder will also be known by VCOPS (might take 5 minutes). Then in VCOPS create a new policy and clone it from 'Ignore these objects'. On association page unfold 'folder' and add your 'LOCALS' folder. Check the "Current effective policy", it should be set to 'Ignore the objects'.
Now every time you add a host into vCenter, make sure you put that local datastore into the correct 'LOCALS' folder. This way you'll exclude them from calculations.