Different post format options per custom post type?

Try adding the post format support on the arguments when you register your post type instead of using add_post_type_support, like this for example:

$args = array(
    ...
    'supports' => array('title', 'editor', 'author', 'post-formats')
); 
register_post_type('gallery-custompost', $args);

See if have any luck.