What a strange thing to do. Probably 100 or more STLs on Thingiverse when one openscad for each external shape would do it if it's written with variables as it should be. In fact one openscad with the shapes commented out and you are where you need to be.
Even then it seems a bit pointless because surely anyone that prints things with any of these 3d printer has done this for themselves at some point.
Still I suppose you have to keep up the thingverse tradition of posting what you did even though no one else can see a use for it.