Plastering a box attached to the wall? Is that some kind of joke?
Why would it be a joke. You create a small stud boxing and plasterboard it then plaster it.
There are no cistern or pipework to be hidden inside, provided you know where the studs are then you can attach the cistern securely to these through the plaster and plasterboard. The boxing would run from the floor up to just above the height of the cistern.
I am confused as to why you could possibly have such an issue with this.
Clearly if you were to conceal the cistern inside then you would leave an access hatch, or pref. not plaster it at all, but on the basis that the only thing to be concealed inside is air I hardly think this a problem!
Looks much neater than a box stuck on the wall just to bring out the wall depth to that required for a cistern to be attached.