I don't think it is possible to force this, especially because you are depending on the user being succesfully logged into icloud. And that there is enough storage available in the iCloud account.
Another approach is parsing the sync status from the ~/Library/Preferences/MobileMeAccounts.plist file and putting the value in a custom attribute so you can monitor if a user has your options enabled. I have not used this myself but my best guess is the MobileMeAccounts.plist file.