How to make the following bbPress function, bbp_forum_class() extensible?

Question

As it exists in it's current form, I cannot easily add custom classes to the bbp_forum_class function like I can with the WordPress post_class.

What do I need to change in the function to make it so I can do the following:

bbp_forum_class( 'my-custom-class')

/**
 * Output the row class of a forum
 *
 * @since bbPress (r2667)
 *
 * @uses bbp_get_forum_class() To get the row class of the forum
 */
function bbp_forum_class() {
    echo bbp_get_forum_class();
}
    /**
     * Return the row class of a forum
     *
     * @since bbPress (r2667)
     *
     * @uses post_class() To get all the classes including ours
     * @uses apply_filters() Calls 'bbp_get_forum_class' with the classes
     * @return string Row class of the forum
     */
    function bbp_get_forum_class() {
        global $bbp;

        $classes   = array();
        $classes[] = $bbp->forum_query->current_post % 2 ? 'even' : 'odd';
        $classes[] = bbp_is_forum_category() ? 'status-category' : '';
        $classes[] = bbp_is_forum_private()  ? 'status-private'  : '';
        $classes   = array_filter( $classes );

        $post      = post_class( $classes );

        return apply_filters( 'bbp_get_forum_class', $post );
    }

I would really like to get the original function modified so that I can add the change to the bbPress trac so that everyone can benefit from this.