[TYPO3-shop] Extra parameters in product link

[Juan Pablo Villaverde]

Hello,

I need to add an extra parameter in the product links in my PRODUCT LIST 
page.
Actually I need to add  &tx_ttproducts_pi1[cat]=2 at the end of each link.

How can I get that? The link part of my template looks like this:

 [ <!--###LINK_ITEM###-->more info<!--###LINK_ITEM###--> ]

I get something like this:
www.mysite.com/index.php?id=32&tx_ttproducts_pi1%5BbackPID%5D=19&tx_ttproducts_pi1%5Bproduct%5D=1&cHash=fb6d277be0
and I need this:
www.mysite.com/index.php?id=32&tx_ttproducts_pi1%5BbackPID%5D=19&tx_ttproducts_pi1%5Bproduct%5D=1&cHash=fb6d277be0&tx_ttproducts_pi1[cat]=2

Thanks in advance.

jp