Bouncing will help, but so will anything that allows the baby space to move (because they do generally try to get themselves into pole position!) and opens the pelvis.
In late pregnancy, there's very little space. If you get on your hands and knees, them drape your arms over your ball, leaning onto it, and relaxing so your stomach hangs down, that will maximise space for the baby to shift around.
To open your pelvis as much as possible, rocking on the ball is good. This is tricky to describe, bear with me! Sit on the ball, feet slightly apart flat on floor. Relax. Try to rock your pelvis forwards, but keep your back straight - it's just the pelvis you want to move. Gently rock forwards and backwards. It helps to relieve aches, and as I say it opens the pelvis giving baby space to move down.
Personally, I think a bit of visualisation whilst you're on the ball, and asking your baby to get in position can help. <hippy >
I did lots of the above for the final month, and went in 8cm dilated, with a baby lined up and ready to go... mostly luck maybe, but I'm sure the birthing ball didn't do any harm!