getting back to global shop after adding to cart

Hi, I realise with different sites contributing to the global shop, buyers will go to the specific site selling the product when they add an item to the cart. How can I best set up the multisite to make sure that after an item is added to the cart the buyer gets an obvious route back to browse for more products in the global shop? At the moment, in my test site, once the item is added to the cart (in a sub domain site) they stay on that site and there is no obvious path back to the global shop.

Thanks

Aileen

http://www.bothybiz.com