For the kneeling, it'd likely be getting down on the knees with the knees splayed apart in a bit of a v.
Then the upper half has similar movement to usual, but the bottom half would only really be able to bounce up and down and side to side - not sure how great that ends up looking, but it at least sounds good.
For sitting, possibly something similar with her sitting on the ground and bouncing the top half with the bottom half basically static. This one sounds like it would look a little silly so might just not be worth trying.
Then the upper half has similar movement to usual, but the bottom half would only really be able to bounce up and down and side to side - not sure how great that ends up looking, but it at least sounds good.
For sitting, possibly something similar with her sitting on the ground and bouncing the top half with the bottom half basically static. This one sounds like it would look a little silly so might just not be worth trying.