Ok, this doesn't work on ALL products.
I wanted to get some more magnets but didn't want to have to pay the extra for the postage as nearly doubles the price. I looked around and found http://www.barfly.com...
I added the magnets and went to checkout - which took me to drinkstuff.com - and I had FREE delivery!
I added some other bits and it still worked - staying under the £35 for free del obviously... but it doesn't work on all items...
It's worth checking anyway... go to barfly.com, add the magnets.. go to checkout.. add the goods you want and check if it's still free delivery - then remove the magnets as I'm sure there not to everyone's taste!
Oh - and you get a free pack of cards still too!
Hope it's useful to someone!