Skip shipping when product weight is 0

Hi,
Currently all products on my site are delivered via email so are all set as virtual which skips the shipping at checkout. Thats all fine.

Now I want to add the option of having the item delivered by post. I think I'm right in saying that adding an attribute for shipping option, selecting post adds to the weight of the product (default weight for product is 0). If The delivery option is Email it adds no weight.

Therefore if all items in cart are selected as email (0 weight) is there a way to have it automatically skip the shipping section just as it does with virtual products?

Thanks

Are your products all Downloads that you now want to offer the option to send by mail?

They're not downloads because they are made to order items. At present I receive an order, produce the item and email it but I would like to offer mail delivery also

You might be better having two different products ...

Otherwise, if you want to use 1 Product with Attributes for:
email it
snail mail it

You would need 0 weight and some kind of weight ... to manage the shipping ...

This would result in Free Shipping freeshipper on orders that you plan to email everything ...