Simple form association custom label name

I have been struggling with what I perceive to be a simple problem:

Working in Rails 3.0.8 with the simple_form 1.4 gem.

I have two models, owners and owner_types;

class Owner < ActiveRecord::Base
  belongs_to :own_type
  attr_accessible :name, :own_type_id
end

class OwnerType < ActiveRecord::Base
  has_many :owners
  attr_accessible :name, :subtype_name
end

In my the _form partial of the Owner view, I want to have a select box that displays both the name and subtype_name of the owner_type association.
....something like this: Owner Type: [name | subtype_name] eg. [Government | Federal]; [Government | Municipal]

My view now contains: app/views/owners/_form.html.erb

<%= simple_form_for @owner do |f| %>
  <%= f.error_messages %>
  <%= f.input :name %>
  <%= f.association :owner_type, :include_blank => false %>
  <%= f.button :submit %>
<% end %>

...the f.association only list the owner_type.name field by default. How do you specify different fields, or in my case two fields?

All help is appreciated; thanks in advance.

DJ