Having worked on that "cake walk" for a few hours, I can say, yes, I can get it to work. However, I'm not sure I can ever make it work in a stable fashion, plus very low density fluid ejected actors at ridiculous speeds. So...never mind.
The other approach I might try would be based on propelling actors to the surface using the collision forces already built into dyn4j, but for that I've got to figure out the walking on water feature. So, probably eventually, but not now.