It's a nice thought, but honestly, there's really nowhere to fit one of these inside the case.  Plus then you also have to worry about the brick transformer and/or customizing a 12v plug for it from somewhere else.

Really the only way this is usefully done is to have the cabling done the way it is.  There's enough room on the outside of the case if you wanted to surface mount one and go that route, but trying to find enough room inside, especially without it impeding airflow (most of the challenge), is quite tough.