make empty checkout button link to back to sub-category

[8020 Design]

when my shopping cart is empty and someone clicks the checkout button it takes you to the main categories page. is there anyway to get the checkout button when the cart is empty to go back to the products page you were originally shopping on (ie, shop.html), instead of taking you to the main category page?

i am using virtuemart 2.0.6, with joomla 2.5.4 - and the website im referring to is http://www.smartsavingslink.com

i would really appreciate any help on this, thanks