I'm not sure that I'm understanding the question..
At the moment global_quote only provides a unique method of shipping if you want additional shipping methods you must use flatrate and conditional actions.
You can disable/enable uc_global_quote using conditional actions, adding new conditions to the "Shipping quote via global quote", but conditional actions doesn't provide much useful filters for a product, just by product type (content type), attribute, or shipping type. Maybe a good option is to add more shipping types and base your Conditions on that, but i think you must write a module to add custom shipping types.
Let me know,