Marketpress multisite yes or no?

Hi, we have a Marketpress install with multisite enabled, as we would like to feature multiple designers on our site, a lot like Etsy.

The problem is there is no manual payments if we enable global cart, and if we disable it the user has to jump from store to store to pay everything, and it gets confusing. Is it possible to at least display a link or something to the other cart/carts on the main page or the main cart, if they contain items, so the user can easily find them and checkout there?