No.
Short selling is not available in this program.
To express the opposite view, you may simply buy the other side of the proposition.
For example, if there are three potential candidates for Mayor in an upcoming election; Anne, Betty, and Carlos and you believe that Betty will lose, you would buy a “No” on Betty, as opposed to a “Yes” on both Anne and Carlos.
In a binary proposition, like the likelihood of a single event occurring, if you do not think the stated event will happen, you’d buy “No” rather than shorting “Yes”.