I would like to propose a database field based upon a SQL query entry box containing some constants such as USERID.
A field with a window where you can type in a select statement.
SELECT c.fullname FROM mdl_courses AS c JOIN mdl_enrol ... JOIN mdl_user_enrolments AS ue... WHERE ue.userid = USERID
In this case, the field will load up all user courses.
Such a field would be very flexible and useful.
Obviously, due to the type of data you could obtain, the plugin would need to be restricted by user privileges.