Codeigniter 3.x / form_input() / preappend or append / bootstrap 3.x

How is is possible to include a prepend icon or an append icon using form_input();

<?php                           
$email = array(
        'name'        => '',
        'value'      => '',
        'id'          => null, 
        'placeholder' => 'Email',
        'class'      => 'mail form-control'
        );

echo form_input($email);
?>
What I would like to do is add, for example, the following bootstrap 3 styling to the email input box:

<span class="input-group-addon" id="basic-addon2">@example.com</span>
I am unsure how that would fit into the array. I have looked at the manual for CI3, however, it does not mention anything in particular. Any suggestions, etc, appreciated.