twenty eleven header customization

I am using twenty eleven child theme. Removed header like this:

function wptips_remove_header_images() {
unregister_default_headers( array('wheel','shore','trolley','pine-cone','chessboard','lanterns','willow','hanoi')
);
}
add_action( 'after_setup_theme', 'wptips_remove_header_images', 11 ); 

?>

Now the question is how do I add my own slider. I wanna use flex slider so the options are:
Via a WordPress hook:
do_action(‘insert_flex_slider’);
Via a ShortCode:
[flexslider]

I am not able to call/place that slider into the header in this site.
http://www.supersolarpanels.co.uk/
Thanks