使现有用户成为Heroku上的管理员

I have installed rails_admin to my rails 3 app which I have set up to authenticate admins based on an "admin" field I added to my User model. Is there a simple way to make an existing user on my Heroku install an admin? I cannot perform SQL on the database because I am currently on a shared DB. Would creating a migration that sets a user(s) as admin be the way to go? Seems kind of like a hack... I have installed rails_admin to my rails 3 app