and it has to run in between the studs, not through them. So that doesn't give you a lot of options. The pipe has to come out of the toilet above, and run in between the studs below, lest you weaken your bedroom ceiling/second floor flooring.
At Christmastime I had some friends over and they wrote on the inside Kitchen walls. I love having people do that. Someday.....years from now.....if this house ever comes down, someone will see all of the love that went into building it.