I've tried what you suggested and I may have done wrong but I can't get it to work. I have a rule setup in discounts so that if the subtotal of items >= 75 they get free shipping. The shipping rule I created from your suggestion was number of items with a specific column value, if the total number of items where free_ship has a value of 0 is = a value of 0 flat rate shipping of $this->GetShipping().
I created a column in the DB called free_ship so items that get free shipping are 0 and those that are not will have a value of 1. If you can tell me what rule I need to create for this or if I can create a rule that says if the total weight is greater that 30lbs you don't get free shipping else you get free shipping.