this is not supported on Fortigate directly.
With so many users and Fortitokens in place, you should probably consider switching to FortiAuthenticator where all this (and much more) can be automated using Remote User Sync Rules.
-Your existing FortiToken Mobile license can be moved to FortiAuthenticator.
-You can test drive the evaluation FortiAuthenticator VM, which comes with 5 free user licenses and 2 free Fortitokens.
-Please reach out to Fortinet Sales for more details or demo.