This is an interesting question.
I do not know LDAP as such, I guess a generic Single Sign-on solution the user could be created and logged in as a potential user, and then it was Moodle that asked the user to accept the policy.
I guess you want Moodle to ask for policy accepting first and second to call the user_enrol method to have to traces of user data if policy not accepted?
Did I understand correctly?
Just as a side note, Moodle deletes non-confirmed users at predefined intervals.
Have you tried contacting the LDAP plugin author directly via a private message on moodle.org or via email (see plugin source code)?
The source code cites Iñaki Arenaza as author. You can look up his profile and write him a message.
You can even make a feature request or some other issue on the Moodle Tracker:
BTW Moodle plugins, including enrol plugins, can have configuration settings, so if you decide to change the setting, consider if it's possible to decide in configuration which approach to use.
I am busy today, but together with the plugin author you can analyse the feature request and see how it fits in Moodle.
If modifying the existing plugin is not an option or it takes too much time, you can also create your own enrol plugin, even temporarily while the original is worked on.
Maybe other users need your version too, so you could publish it also.