Returning Giveaways

Is there any possible way "return" giveaways you have won? This is just in case you've entered two with the same game and (in the unlikeliest of chances) won both. Is there also anything in the random choice system which checks which games you have already won/you already own so it automatically removes your name from the list of entrants?

Let's say I enter two giveaways for Counter Strike (there seems to be quite a lot at the moment). The next time I visit the website, I find out that I've won both giveaways. Will there be any way of telling the website that you don't want the game anymore, allowing another member to be randomly chosen?

Sorry if none of this makes sense. TIA.