No, I think you misunderstood. SP is tightly coupled with the upvote and downvote mana. This means that you can only delegate SP to others that you haven't used/spent to vote. If you buy/get a delegation from others, your upvote and downvote mana increases as well. It's not directly possible to delegate or rent a downvote. If you want your downvote mana to be "used", you could join a flag trail. If you believe you found a post/comment that deserves a flag but haven't the SP to handle it yourself, you could try to reach out other more powerful curators, the @steemflagrewards team or steemcleaners (depending on type).