Couldn't you set up a fake account without any followers and blast it that way? It technically would still even support the artist, as the hashtag could still start trending.
I tried it. You can't keep spamming the EXACT same tweet over and over again otherwise Twitter pops up an error message saying that I have to tweet something else before that tweet can be sent. But I think it's a certain time limit because even after I tweeted something new, it still wouldn't let me send the sweepstakes tweet. Nor can I change the tweet in anyway because that goes against the "Official Rules" of the contest.