How to turn off Length Error messages on Password Confirmation fields in Authlogic

In Authlogic, if you use a password confirmation field (when creating a new user perhaps), there is an error message that shows up for that field if the User model does not validate.
Something like

is too short (minimum is 4 characters)

Seems simple enough to turn off, but I almost went mad trying to figure out how do this without completely turning off password authentication.

class User < ActiveRecord::Base
    acts_as_authentic do |c|
         c.merge_validates_length_of_password_confirmation_field_options  :allow_blank => true

PS: It’d be nice to get all the configuration options for Authlogic in one place, with better documentation for each one.
Maybe I should get on that … it is open source software after all