Fill a large glass (approximately 20 ounces) with the slices from 4 lemons. Add vodka and allow to set for 15 minutes.Using a muddler or similar instrument, muddle lemons thoroughly. Your lemons should be shredded when done.
To two tall drink glasses, add 4 ice cubes to each, add half of the remaining lemon slices to each, pour half of the lemon vodka mixture through a strainer and into each glass. Add 4-8 ounces of 7-Up to each glass; stir gently to combine, and serve cold.