Instead, I was contemplating this sort of change to Empty Space:
Alas, this doesn't work as you can just use a climber (or even builder for Ramon's solution) from the inside of the box to elevate the bomber hole.
Can we rename Cuber Replacement? Previous levels do not suggest that cubers in particular are the go-to tool for making a digger continue.
I think the name is rather appropriate as the player places a cube and something that very much resembles a cube (a replacement, or alternative or maybe you can find a better word) in the level. I don't see any allusion to the cube as go-to tool for continued digger in there.
Or Maybe "Build Your Own Cube" or something like that?
Attached is a version of Sinking Ship that should eliminate Simon's solution. Please tell me if it still looks like you can get close enough to the requirement to try pushing this solution through.
EDIT: If this is not good enough, attached is an even more extreme variation (V2b), it's also a bit uglier.