You won't find answers in philosophy, that's not what I'm debating here. We cannot see an electron either, yet we know it exists. Can we be absolutely sure that it is what we think it is? No but our theories allow us to manipulate it, to predict its behaviour and to use it as the foundation of other theories. Layer upon layer of assumptions based on evidence, mathematics and experimentation is what science is and it's the reason why it works so well to describe the world around us. Every piece of evidence we have suggests consciousness is indeed contained within the brain. Your hypothesis is an invalid product of pure imagination, unless new evidence is found.
In other words, "anything is possible". This self-defeating ideology, if I can call it that, brings nothing to the table when trying to understand things because it creates false equivalents. An example: before we understood what lightning actually is, there were a large number of possible explanations. The main ones, "Zeus did it", magic, "Wrath of God", existed along with explanations such as a type of naturally occuring interraction, not fully understood at the time. "Anything is possible" dictates that we consider all of these explanations and avoid to rule them out. The first ones are based on imagination, with no evidence to back them up. The latter is based on the observed effects of lighting (such as fire) and, curiously, turned out to be the correct one.
And so it goes with your current I'm-just-making-things-up hypothesis. You can, of course, obliterate my argument by presenting just one piece of evidence suggesting that consciousness exists outside the brain, but we both know you can't do that, don't we?