Shipping is Free if the Product is Free

I could have sworn I saw this as an option somewhere in ZC, but now I can't find it.

I'm setting up a DVD retail/rental store. I want customers to be able to choose Rent It as an attribute. That choice would make the product free. I would want shipping for that order (they have to complete the check out process to send in their wishlist for rentals) to be free.

I've tried subtracting the weight of the product in the attribute controller but then the checkout process hangs up at step 1 of 3.

I have a private ssl certificate for my checkout if that makes any difference.

Any help would be appreciated.

One trick is the 0 weight means Free Shipping ...

Set the Rent Attribute to have a negative weight equal to the Retail weight ... then when it is a rental the weight is removed from the order so the Product is 0 weight ...

Now on an order of 0 weight ... turn on the Free Shipping (freeshipper) module and be sure that in Stock Settings you have 0 weight marked for Free Shipping ...

On mixed orders, the Rentals will apply no weight to the order so they will still be free if someone orders 12 Rentals and 1 Retail item ...

I tried that...that was my first logical choice actually. But when I put a negative weight in the attribute, the cart hangs up at step 1 of 3 and won't complete the check out.

1 Turn on the Free Shipping (freeshipper) Module

2 Set the setting that 0 weight means Free Shipping

did that too. Now it's hanging up even with my download products (where I've subtracted the weight so there's no shipping charge for the download).

Ok...got it running. Next question is in the attributes forum.