Add field formatter settings to all field formats
I've managed to work this out.

hook_field_formatter_info_alter() isn't properly implemented in Drupal 7. There is however the field_formatter_settings module which exposes two hooks:


hook_field_formatter_settings_form_alter()
hook_field_formatter_settings_summary_alter()


https://drupal.org/project/field_formatter_settings

Using the dependent modules (e.g. field_delimiter) as examples I was able to achieve what I needed.