Setting a message on a model -without- errors.add_to_base

I'm trying my best to follow the skinny controller/fat model concept,
and I've got a series of callbacks (that I'm about to move into
observers) running on a few models. Based on what these callbacks do
to the data (it's implementing business rules), I'd like to add some
type of message on the state of the model *without* invalidating it.

For example:

class Order < ActiveRecord::Base
  after_save :do_something_cool

  private
  def do_something_cool
    # manipulates the order object in some way based on business rules
    errors.add_to_base("Message about what we did to your order to
match said business rules")
  end
end

I'd prefer to do this without calling errors.add_to_base, because it
isn't an error. Furthermore, I don't even think that works because
it's being called -after- the model is saved (so far, even though the
callback in my case is running, it doesn't appear to be adding
anything to the base errors object anyway).

Obviously I can't set flash[:notice] inside the model as it's owned by
the controller, and I really don't want to do some insane hacking to
incorporate elements of the controller into the model (that would
really make this spaghetti code and kill performance!).

The only thing I've thought about so far is setting a virtual
attribute of some kind, but I'd like to see if anybody has a better
idea before I jump straight to that.

Any thoughts on the matter? Thanks for any input you can provide!

I think a non-DB ("virtual") attribute is a good idea.
Simply declare the attributes with attr_accessor.

class Order < AR::B
  attr_accessor :my_attribute
end

This will add the initialization of the instance variable and create
getters and setters.