In specific, I thought that using を twice in the same sentence was forbidden but here it is used 「素晴らしいということを有名人を使って。。。」 →　You are correct and it is certainly forbidden to use を twice in a sentence. However, you can use one を per verb and a sentence can have more than one verb. It is because a sentence can have a main clause and subordinate clauses. In this case, "素晴らしいということを(object)　放送する(verb)" and "有名人を(object)　使う(verb)". さらに、「理想の自分を追い求める」生き方が素晴らしいということを有名人を使ってマスコミが大々的に放送したり、「私はこれで成功した」という「ハウツウ本」が本屋に氾濫しています → Furthermore, the media use celebrities and highly broadcast how wonderful the way of life which "chasing one's ideal self", and the bookstores are flooded with how-to books of "I have succeeded this way". I hope my translation makes sense.