There is currently no way to demote Administrative users to regular users.
What you can do is set up a group of dbFront Users and exclude administrative users.
This would force those administrative users to use their regular network account to access dbFront.
This would only work in those environments where Administrative users were given both a regular network account and an administrative account. e.g. "Fred.Stuart" and "Fred.Stuart_admin".
NOTE: Giving Administrators two accounts (Admin, NonAdmin) is a highly recommended best practice.
See: Security Group Setup