Free shipping for selected items

[RiverValleyTrading 13]

Hi all, 

I always run promotions on certain items where  you get free shipping on your entire order if you purchase a certain item. However,  if the buyer adds in other items then the shipping cost addin automatically. It's up to the buyer to change the shipping to Zero. Is there a way to have it so order shipping will be free if the order contains a certain item?  It would make life so much easier, rather than keeping track of credit notes for each customer who paid the shipping mby mistake. 

Any thoughts / suggestions?