Free shipping specific products via media mail

My client wants to do a promotion that offers free shipping on certain products when shipped via USPS Media Mail.

They still need to be able to select another shipment method, for example FedEx overnight, of they want to, and be charged the proper amount.

All other products still need to charge the correct amount for Media Mail.

Any help is appreciated!

I got it! Ithought I'd post anyway in case anyone else looks this up, or to save any good samaritans the trouble of typing:

It was simple: I just checked "Always Free Shipping" for each item, and enabled the Free Shipping option. The "always free shipping" sounded deciving to me, as I thought it would not offer any other paid-for shipping method, but it worked exactly the way I need it to...