Well you could create extra users from the manage MySQL page under Goodies then click on the user under 'Users with Access'. This will open out to the permissions page and I suppose if you deselected the lot then phpMyAdmin would not be much use to that user.
I have not had need to use this but it should work. If not it is something else to blame on the government!
Opinions are my own views, not DreamHosts'.
I am NOT a DreamHost employee OK! :@
Act on my advice at your own risk!