Honestly dude, how can you compare nutriet uptake to water flowing up or down a hill? When you feed your plant, you're not pouring water down a straw and you're not pushing it up a straw so it doesn't really matter which way gravity is pulling. Nutrients are taken in by the plant as needed. It won't matter if the plant is upside down or sideways...For the sake of argument, let's assume it might make a difference, that difference will be so minute that it won't make any noticable difference and will be a waste of time. Imagine growing more than 1 or 2 plants like that.
Also, as far as the gravity issue, it would work against you in this situation. If your plant is upside down, and assuming you plant it like you would if it was right side up, your roots couldn't grow down because there's no soil there, so they gott grow up while the water goes down. So if you're watering from the top and gravity is pulling the water to the bottom, doesn't really matter if it's upside down or not, now does it?
Let's assume you plant it deeper to give the roots some room to grow down. In this case, what difference would it make if your plant is right side up or upside down if both the roots and the water are being pulled down by gravity the same way if it's right side up.