Think about how a torque converter works on a car. Centrifugal force creates enough fluid drag via pressure to propel your vehicle. Inside the spinning tube will be no different.

I think the solution would be to use a heavier oil (sticks to things better) and then have the gears protrude into where the oil is being held on the sides of the tube to splash it around, or at least become bathed in it as it passes through.

Too much, or too thick of oil will cause excessive resistance (especially cold) that will waste engine power, so that's another concern to think about.

And, yes, I am aware thinner oil lubricates better.