List non-empty categories from a custom post type

I have a Custom Post Type that uses the default category, the same as the posts, and some other post types in my site. How can I list all non-empty categories from the custom post type?

For instance, if I have categories “Cat 1”, “Cat 2″ and “Cat 3” and I have a default post with a category of “Cat 1″, and a custom post with categories “Cat 2” and “Cat 3″. How would I write a function that would return “Cat 2” and “Cat 3″?

It seems like the get_terms() functions don’t support a post_type argument. Is there a way I can add some other query to a get_terms() function?

I know that it is possible to hide unused terms:

$terms = get_terms( array(
    'taxonomy' => 'category',
    'hide_empty' => true, <-----
) );

However this hides empty for all post types, I’d like to hide empty for just a custom post type.