How to put free products in cart?

[jdesign]

Hi,

I would like to make a cart for each of my client to put free product inside. The problem is that when I change my product to 0.00$, the cart disappear. We already have ours clients and they do a payment monthly for our service so I don't want to put price to my products and bill. I just want them to choose the product they need and put a copy in the cart so they can see which products they choose. In the version 1.9 of virtuemart, i found on the web a way to change this by the php file but I find anything for the version 2.0 of virtuemart. Can someone help me please?

Thanks!