This dose would be the one file that you would give out for free, and I'll explain why. It would be short, and produce an experience that doubters would be sure is not a placebo, so they would be persuaded to buy a dose.
It doesn't have to resemble any particular experience. What it must do is simply confuse the brain, so that it would do something, anything, that would tell people "This is for real." It might produce a sense of euphoria, or of confusion. Perhaps even pain or fear, just to show that binaural audio can really influence the mind. There might not even be a need for a description of what it does.
This would first of all bring much more traffic to your site, since potential visitors come, attracted to the idea of getting started quickly, and being able to know it is for real. You could put up advertisements on the download page, just so the inevitable fraction of site visitors looking for a free ride would not be a lost cause for you.
I'd like to know what you think of this! Thanks for reading!
Convincer
That seems like a pretty good idea, except for the fact that it probably won't work. Think about the first times you tried I-Doser, probably didn't work for you right? What would be a good idea is to advertise the free doses they already give out. Or to make one dose of your choice (except for doses over five bucks) free, when you sign up at the store.