Originally Posted by artemis

While you can give your Companion Pass away, trading airline miles violates the terms and conditions of most frequent flyer programs. You may not care if your Southwest frequent flyer membership is canceled by the airlines since you don't intend to fly on them, but you will care if your membership in whatever airline program you've traded your Southwest miles for is also shut down. The trade could potentially leave you with nothing.

Why not find a way to use up the Southwest miles you already have (you may be able to cash them in for something other than flights), or donate them to charity if you really don't want them?