Is there anyway to render SpriteShape inside of one Big Sprite

I have auto-generated level for platformer, at this moment it displays by LineRenderers like this:


But i wanted to use SpriteShapeRenderer to fill all empty space around of my level and also to draw some kind of platforms surface for my level. So i need a way to apply SpriteShapeRenderer as mask for one big sprite.

Not sure what the best way to do it...

I thought that i can do it someway like this:


But it doesn't works... Sprite Shape surfaces applies only for Sprite Shape and doesn't works with Masks =)
So here what i got:


But i wanted to display platform's surfaces inside of mask.

I know that i can build Sprite Shape in this way but it looks like a hack:

Can someone advise a best way to do it?

Thank you!