Shipping cost Base Free

Hi,
I make my catalogue products and I have a problem.

I have :
Physical products (objects) need Base / Fixed shipping cost
+
Numerical / Virtual products (formations) need Free shipping cost

I tested to cancel the Base shipping cost for my virtual products with the individual code : shipping=”0.0001″ and also 0.001

But, it doesn’t work. Did I something wrong ?

How is it possible to cancel Base shipping cost when person order just Numerical produts ?

Base shipping cost are very useful for me because I can not give an individual price for each physical objects (too fat and too expensive solution).

How can I do free shipping for my Numerical / Virtual products, please ?

https://wordpress.org/plugins/wordpress-simple-paypal-shopping-cart/