The problem: "Since the brain in a vat gives and receives exactly the same impulses as it would if it were in a skull, and since these are its only way of interacting with its environment, then it is not possible to tell, from the perspective of that brain, whether it is in a skull or a vat"(from wikipedia)
So, to just use the example of an eye connected to a brain, the eyes receives light, which is then transmitted to the brain. The skeptic would say how do you know you are actually seeing things with your eye, and its not just transmissions directly to the brain.
My "solution" would be to imagine what type of machine could "fake" the transmissions to the brain without actually seeing. This machine must be cabale of causing the specific "transmissions" (whatever those are) that produce phenomenal visual experience to go to the brain. These transmissions cannot be uncaused, but in order for them to create the specific illusion of visual perception in the brain, the causes would have to be identical to those that are normally produced by the eyes photo receptors. Therefore, in order to create an illusion of reality, the machine would have to be identical in causal function to an actual eye, but it that case there would be no illusion, but just actually seeing (with some sort of cyborg eye machine). Does this make sense and is it a legitimate solution?
I have also tried to explain what I mean more clearly in comments.