Have one of those large rubber things sitting around your house? Feeling guilty for not using it or putting it away?
Well, it makes a spiffy weight bench for presses. Sit on the ball and walk your feet forward letting the ball roll underneath you until your head and shoulders are supported. The rest of you, you hold up using your abs and thighs.
I've been kind of lazy so I haven't tried kickbacks or anything on the ball, plus those can be done with good form on the floor, so a bench isn't as vital.