What is the best way to add a link to checkout in the menu

I am setting up marketpress for a client on a development server. I'd like to have a link to checkout as one of the menu choices, but since it's not an actual wordpress Page, my only choice seems to be to add as a custom link...which takes the full URL...which will be different on the live server.

This seems like an obvious need...what am I missing? Is there some way to use the shortcode in the menu?