This and a few other settings exist only in an XML file within the user's roaming profile folder. What I have suggested to other customers is to create a logon script that seeds a generic file to this folder if one does not already exist. You have to be careful not to let the script overwrite the file as that would erase other preference changes the user makes.
One other irritating limitation: The calendar integration preference is not in the XML file; it's a database field. Enabling that globally requires a SQL update from the server CLI and must be redone after you add new users.
