On my Ecommerce i've just added it in robots.txt
You should be able to do something similar. Below is what I have but I use x-Cart as my ecommerce site.
User-agent: *
Disallow: /printable=Y
Disallow: /js=
Disallow: /sort=
Disallow: /sort_direction=
Disallow: /product.php
Disallow: /home.php?cat=*
Disallow: /catalog/
Disallow: /search.php
Disallow: /cart.php
Disallow: /help.php
Disallow: /giftcert.php
Disallow: /product.php
Disallow: /orders.php
Disallow: /register.php
Disallow: /icon.php
Disallow: /image.php
Disallow: /error_message.php
Disallow: /offers.php
Disallow: /product_image.php
Sitemap: http://www.domainurlhere.co.uk/sitemap.xml