I see what you guys mean. But in this case, wouldn't it be simpler to just pre-cut several sheets at a given height, leaving the wires and power outlet assemblies till last moment, maybe temporary fasten the wires about the position where the outlet holes will be located. And use the wall integrated types of power outlets instead of the external types?
I don't know about your country, I don't know about basic electrical work either, but here in Sweden we use these "casings" for integrating power outlets into plaster walls. It's like a round cup of plastic with a hole in it, where you stick the cables leading out of the wall, and then onto, or rather into this cup you insert the power outlet assembly.
You know what I mean?