How can I let users open the site for other visitors?

Based on Bainternet’s answer to this question:
Save Theme Options (options.php) From The Frontend

The key is to know the name of the plugin option to Enable/Disable the Maintenance Mode.
In this example, it’s named: my_maintenance_mode

<?php 
    if ( isset($_POST['mmode']) && isset($_POST['action']) && $_POST['action'] == "update_mmode" ) {
        if ( wp_verify_nonce( $_POST['theme_front_end'], 'update-options' ) ) { 
            update_option( 'my_maintenance_mode', $_POST['mmode'] );
        } else {
        ?>
            <div class="error"><?php echo 'update failed'; ?></div>
        <?php
        }
    }

    // DISPLAY FORM ONLY FOR THESE ROLES
    if( current_user_can( 'administrator' ) || current_user_can( 'editor' ) ) {
?>

<form id="save-mmode" name="save-mmode" action="" method="post">
<select name="mmode">
<?php $selected = get_option('my_maintenance_mode');
    <option>Enable/Disable Maintenance Mode</option>
    <option value="1" <?php if ( $selected == 1 ) echo 'selected="selected"'; ?>>Enabled</option>
    <option value="2" <?php if ( $selected == 2 ) echo 'selected="selected"'; ?>>Disabled</option>
</select>
<?php wp_nonce_field( 'update-options', 'theme_front_end' ); ?>
<input type="hidden" name="action" value="update_mmode">
<input type="submit" name="update-options" value="Save">
</form>

<?php
    } // END if(current_user_can)
?>