empty skin as a mold

Hello everybody,Here is a challenge (or at least it is a challenge for me)

I am currently doing a ring of diameter 60cm and the technique is to cut it in 8 parts that are printed hollow, with a wall thickness of 1mm and then I cut their tops and bottoms leaving a frame of apx. 5mm to glue them together.
Then, the hollow model is pured with concrete to create the final sculpture and the pla is removed with a scalpel. (this is a technique I've used a couple of times and works perfectly)The challenge is that currently I open the top and bottom of each piece by hand (left image is just before I cut the openings) which consumes time and doesn't give a clear result.Do you think there is a way to do it automatically?What I want to do is print a skin like the picture on the right (of the first image).


I thought of taking the skin, giving it a thickness of 1mm in the 3d program and printing it at 100% infill (treating the 1mm wall as a solid object from cura's perspective) but this poses challenges to achieve in my 3d program.

Do you think I could achieve this by using some kind of boolean operation within cura?(to explain: print it as a solid with 1mm thickness and 0% infill but use a second solid that would tell it which parts NOT to print.)
(i.e. the yellow piece is to be printed and the orange piece is a 'negative' that will not let cura print in the space inside it)

given that you are already printing a hollow model - I really don;t understand what the right hand image is showing ?

And when you say you open the top and bottom - what do you mean ?
The top and bottom are already open.

What i would do, is to print two of the sections with a hole along the 'top' or 'bottom'.
Then when you glue the ring together, you have two holes: one to feed the cement into and one to let the air out as the ring filles up.

So I think I need more pictures to understand the problem, as i can't see one.