Create New Sub-Nav Item with own function

I have installed this "Posts on Profile" plugin that shows the list of posts made by the users by adding a "Posts" tab to user profile navigation. Here is the link to the plugin:
http://nxsn.com/projects/bp-posts-on-profile/

Now, what i want to do is add a new sub navigation in the "Posts" navigation with my own function. I tried this with no avail:

function posts_subnav_hook() {
    global $bp;

    bp_core_new_subnav_item( array(
        'name' => 'Create New Post' ,
        'slug' => 'create',
        'parent_slug' => $bp->postsonprofile->slug,
        'parent_url' => $postsonprofile_link,
        'position' => 10,
        'screen_function' => 'my_own_function',
        'user_has_access' => bp_is_my_profile()
    ) );
}
add_action( 'wp', 'posts_subnav_hook', 2 );
add_action( 'admin_menu', 'posts_subnav_hook', 2 );

Here is the core file of the plugin:
http://pastebin.com/mhTa4KHp

Please Help!!