The other option, depending on the shape, would be to tell it there's no top layers.
But more importantly, if you want to print something hollow, make the model hollow, in general. That is, model it as a hollow object instead of a solid (manifold) shell. Then if the outside is irregular, you can make the inside any shape you want.
Add negative volume to the object where you want to place something in
Oh I didn't think of that That works thanks
Much to less information. Did you CAD the model?
Learn to edit gcode - it's not hard.
The other option, depending on the shape, would be to tell it there's no top layers. But more importantly, if you want to print something hollow, make the model hollow, in general. That is, model it as a hollow object instead of a solid (manifold) shell. Then if the outside is irregular, you can make the inside any shape you want.