How make a passage traverse staves

I'm working on typesetting a very challenging score that may spawn about three more forum threads after this one! My first question is how to emulate the passage shown below, in which the piano left hand goes very high and the composer has written the upper notes in the treble stave.

I think I could add the higher LH notes into the RH stave as Voice 2, with corresponding rests in the LH, then hide all the extra rests, but I think this would (I think) prevent beaming the sextuplet semi-q's together. I've also thought of writing the high notes an octave down in the LH stave and using an 8ve, but it's better as written by the composer.
Any suggestions?