I have got very small steps working with passive hips and ankles for leaning sideways. I always thought I didn't move that much side to side when I walked myself anyway - it was just about getting the timing right, even a few milliseconds here and there made all the difference.
Future will be:
1) moving the hips slightly to make bigger steps (more time between swing from side to side), even loosening the hips on springs will probably give the desired effect.
2) Actively moving the hips and adjusting the timing dynamically depending on how far it swings side to side to keep it on balance and stop it getting 'carried away'. This will be active balance.