[Plugin: Microkid's Related Posts] Multiple posttypes?

The following shortcode only shows related posts of that posttype:

[related-posts posttype=page]

Is it also possible to show posts of multiple posttypes with a shortcode? Something like

[related-posts posttype=page,post,custom_post_type_1]

The above method does not work, any suggestions? It seems to be possible to achieve this with an API function but I’d need a shortcode.

http://ww.wp.xz.cn/extend/plugins/microkids-related-posts/
http://www.microkid.net/wordpress/related-posts/#API