Alpha sorting on both options and groups for option_groups_from_collection_for_select

# How would you best perform a secondary sort on :buildings below?
= 'Building Name'
= select_tag 'building_id', |
  option_groups_from_collection_for_select(Site.all(:order => :full_name), |
  :buildings, :full_name, :id, :full_name, nil) |