Remixed the “Kallax Hider” to include hinges that can be attached to the inside using double-sided tape.
Thanks to @Celta and @Nui !
The file “Kallax-Hinged-Door-Complete” is just to have a fancy 3D preview here on Printables.
Reversible Hinges are glued on, as I found no good way to add them in a workable state directly on the parts. And as Kallax is only cardboard from the inside, screwing in them isnt really desirable anyway.
I'am currently printing the parts, I have not tested them yet!