Using a wooden tool (the "muddler") to crush the limes and mint together, so the juice from the limes mixes with the mint oil.
Muddling is usally done with drinks that involve fruit and/or sugar, to crush the fruit or sugar cubes in order render a fresh taste, before adding ice and spirits (e.g., an old fashioned, a mint julep, mojito, etc.). If you just used a blender, for example, the taste wouldn't be nearly as strong, and you'd also be picking mint out of your teeth for days.
Muddling is easy enough to do, but you generally need to do it from scratch with every new cocktail, which is why I asked if any body had a volume approach.
http://www.drinkstuff.com/products/product.asp?ID=403#