Hi silvia,
Thanks for taking the time to submit this idea.

In the meantime you could achieve this by creating a new Product Group for your free products, and moving Weebly Free into that Group.
Next, activate with the Bank Transfer or Mail in Payment modules, setting the display name to something like "No Payment Required" or whatever you prefer.
Finally, edit the Product Group, and assign just this gateway module to it.

This way clients will be able to order and checkout without being prompted for card details.