I have a partial solution where I can add a image crop uploader to the theme customization page. I have yet to figure out how to attach it to acf.
function add_my_media_controls($wp_customize) {
$wp_customize->add_section( 'theme_banner_image', array(
'title' => __( 'Banner Image', 'theme_banner_image' ),
'priority' => 35,
) );
$wp_customize->add_setting('banner_image', array(
'type' => 'theme_mod',
'capability' => 'edit_theme_options',
'sanitize_callback' => 'absint'
));
$wp_customize->add_control(new WP_Customize_Cropped_Image_Control($wp_customize, 'banner_image', array(
'section' => 'theme_banner_image',
'label' => 'Banner Image',
'width' => 2000,
'height' => 1200
)));
}
add_action('customize_register', 'add_my_media_controls');