How do I set shipping charges for carts with zero weight?

I want to set a default shipping charge for products with zero weight. Answer: create a shipping rate line for a weight of 0.

Assuming weights are in grammes and the currency is pounds sterling then the following lines will add shipping charges as follows.

For country group 1: 99 pence for carts with zero weight and £1.20 for carts up to 100 grammes.
For any other country ( using country group 0 ): £9.99 for carts with zero weight and the same for carts up to 100 grammes.

0|0.99|1
100|1.20|1
0|9.99|0
100|9.99|0

Note: These are simple / unrealistic examples.