How to properly pass collection for input in Formtastic

I need to pass a collection to the standard select input in Formtastic:

f.input :apple, :as => :select, :collection => Apple.all

The problem is, though that I need Formtastic to access a different method than name. Now this is really a problem. I can always pass the Array

f.input :apple, :as => :select, :collection => Apple.map { |a| a.format_name }

The problem is, that after this I will get strings in the controller instead of IDs which is not desired. I tried to pass Hash instead:

options = Hash.new
Apple.each { |a| Apple.store(a.format_name, a.id) }
f.input :apple, :as => :select, :collection => options

Now the problem is, that since I am using Ruby 1.8.7, the Hash order is unspecified and I of course need ordered input...

I can imagine some solutions, but all of those require unnecessary code.

Any idea how to solve this right?