How to set the default value on a simple_form association

Folks
  Im using simple_form and im able to see a selection of users from my
drop
down list but im trying to set the default value. Here is what ive tried
<%= f.association :people, :input_html => { :value => 'someval' } %>
i want someval to be set in the selection by default. Any help would be
appreciated.