Yes, remove the shipping calculations that you don't need and create a new one.
When setting up shipping rules, there are three sections:
1) Name
2) Triggers
3) Calculation.
Set the name something like "Shipping Rate"
In the triggers selection, click the plus button to add a trigger.
From the select list of available triggers select "Based on total Number of unique items".
In the form below the select enter:
If the total number of unique items in the cart is ">" a value of "0"
In the calculations section, select "Based on column subtotal" from the select list of available calculations, and fill the form in as:
Subtotal Column of "TotalWeight" "Plus" "0"
