Would it be possible to show the sand "falling in" and the Sarlacc mouth itself opening up from within the hole? It would certainly establish that there's a large creature under the dunes, and would allow for the removal of the beak. It's a lot of effects work, sure, but would it even be possible?
And Monroville, your suggestion #3 is a great idea, either instead of or in addition to showing the "monster" coming to the surface under the sand.