I would advise against it.

CO is serious stuff and a balcony is just too close. Also your going to want to refuel it up there and again, it is just too close for comfort.

A fire from a little spilled fuel or CO poisoning and you will wish your only problem was a lack of power.

Put the generator some distance away. Twenty-five feet isn't too far. Determining the safe distance is a matter of the specifics of the situation and judgment.