Static gluteal activity by holding ball against wall side on and thoracic rotation

Stand with your side onto the wall and use gentle outward pressure of your leg to hold the ball against the wall.

Lift your inside leg off the floor with your knee bent and gently push the ball against the wall with this leg.
In this position cross your arms against your chest and bend forward and away from the wall by using your thoracic spine. 

Keep your hips square and your pelvis and lower back stable.