Question How do I mold the shape of a hole with worldedit?

So I have completely excavated and brushed up a large (as in like 150 blocks across, 50 deep) bowl shaped hole on the surface of the world for a project where essentially a chunk of land is floating in the air. The problem is, I don't know how to make the floating part similar to the hole.

I was thinking that I might be able to fill it with sand, select it, replace it with say, bedrock, then move it up?

I'm not sure if that's possible at all, but any help is appreciated!