If I were you, I would not start hanging stuff off the guitar's soundhole.
Unless you are willing to screw a strap button into your guitar, you should probably forget about playing it standing up. As another user mentioned here, classical guitars were never really meant to be played standing up, which is why it was not designed with strap buttons in the first place.
If I were you, I'd leave it alone. Drilling holes into it and making alterations of this kind could damage the finish, mess with the guitar's tone, and lower the value of the guitar.