I tried this experiment, and it worked. But only a little. I would say that about a third of the bad taste for me was masked by stevia ("Better Stevia" from Now, pure extract of the stevia leaf).
But that still leaves something that causes a 66% nausea in me. How do others feel about Soylent 2.0? How do you feel after you add sugar or sugar substitute?
One problem with stevia testing is that it is hard to get just right because it is so intensely sweet. But the artificial sweetener that Soylent uses is a modified form of sugar that should be easier to use in testing, due to its being less critical in its amount.