Formating default data for text fields

Here's my setup:
In migration file:

...
t.column :perm0, :int, :default => User::Perms::Base, :null => false
...

(User::Perms:Base = 1)

In app/views/login/add_user.rhtml:
...
<label for="user_perm0">Permissions:</label>
<%= form.text_field :perm0, :size => 10 %>
...

While (quite magically), provides me with a form with the default
value "1" helpfully prefillled.

The fly in the ointment is that, should I decide on a more interesting
default, I'm going to want the value displayed zero-filled in hex
(%08x instead of %d). Any ideas?