Hi Jim,
Thanks for the very kind words in regards the plugin, they are much appreciated!
If you select the shortcode option you can switch between menus using some sort of PHP code, in fact I have written about this exact issue on the following page of my site:
http://peterfeatherstone.com/wordpress/responsive-menu/faq/shortcode/options/
Please check the above and let me know if you need any further guidance.
Many thanks
Peter