Magento

Your help would be appreciated…

I would like to offer flat rate shipping for shipments to the U.S. However, I have numerous products that are very heavy and need to have the shipping prices customized (nont included in flat rate shipping). Is this possible? I can’t seem to find any way to do this, but I can’t imagine its not possible. 80% of my products will go at the flate rate shipping rate, but I need a way of setting exceptions and inputting (even if its manually) shipping prices/options for the heavy products.

Thanks for you rhelp!