Jeremy Herve on "[Plugin: Jetpack by WordPress.com] Share images, css & js not loading from subdomain."

Once you've checked the "Disable CSS and JS" option, you will be able to manually enqueue your own sharing js and css files.

Jetpack uses the WP_SHARING_PLUGIN_URL constant to build the path to load the libraries. You could change that constant by your own when re enqueueing the sharing libraries, like so:

function tweakjp_add_sharing_js() {
    wp_enqueue_script( 'sharing-js-fe', YOUR_OWN_WP_SHARING_PLUGIN_URL . 'sharing.js', array( ), 3 );
}
add_action( 'wp_enqueue_scripts', 'tweakjp_add_sharing_js' );

function tweakjp_add_sharing_css() {
    wp_enqueue_style( 'sharing', YOUR_OWN_WP_SHARING_PLUGIN_URL.'sharing.css', false, JETPACK__VERSION );
}
add_action( 'wp_enqueue_scripts', 'tweakjp_add_sharing_css' );