This worked, but some developers on the team didn't like the (arguably) unnecessary additional syntax. These developers argued that since none of our Unit Tests hit the database we should simply override the new method and handle stubbing the columns method.
You can argue that adding magic to the new method could be confusing, but our team has the standard that no unit test can hit the database. Therefore, everyone is very aware that, despite the standard syntax, we are injecting our own column handling mechanism.
The code to make this work is fairly straightforward. The usual alias method gotchas apply so I chose to use an alternative. Adding the following code will allow you to create disconnected models in your unit tests simply by calling new.
class << ActiveRecord::Base
new_method = instance_method :initialize
define_method :initialize do |*attributes|
attributes = attributes.empty? ? nil : attributes.first
def no_db_columns attributes
return  if attributes.nil?
attributes.keys.collect do |attribute|
sql_type = case attributes[attribute].class
when " " then "integer"
when "Float" then "float"
when "Time" then "time"
when "Date" then "date"
when "String" then "string"
when "Object" then "boolean"
ActiveRecord::ConnectionAdapters::Column.new(attribute.to_s, nil, sql_type, false)