[dTal]

Not quite the same, but my dad did an alcohol study once where the blinding was achieved by giving the test group a strong vodka-and-orange, and the control group a glass of orange juice into which had been poured a small amount of vodka over the back of a spoon, so that it floated on top. Both drinks therefore smelled strongly of alcohol.

It's trickier with substances where the dose is undetectably tiny, but it seems there's certainly value in making people feel "trippy" so that they think they've had the active substance.