You can get a bit extension and attach it to a long auger bit. You'll need to setup some sort of guide block to have a chance at getting it straight down the run. If you have a lathe, that would make it easier to even out the wall thickness after drilling. Make sure you do a test run.
Like one of these? I think it only really works with spade bits, but I bought one and used it one time. Its never been touched since.