One way to do that is to make 2N packages containing a spiked and a non-spiked sample, with one sample marked 'take me first', and, in N cases, have the LSD-spiked sample be that sample. Of course, if you do that, it is even more important to not inform the subject about the history of he experiment before it is over.
I see. So you were suggesting throwing in a categorical variable for the day of week and including that as a additive covariate to control for fixed-effects on days. I haven't actually run into any of my experiments depending on day of week to any important degree, but I still try to avoid 7-day blocks to make that less of an issue. It's not like there's usually an advantage to running in a weekly block, so better safe than sorry.
Yes, I'm aware of the statistical concept, and do controlling in a few other essays. My point was: 'control' is not an instantly obvious application. What am I controlling and how? Am I modeling it as a separate additive categorical variable? Quantitative variable? An interaction? (All different in R's formula notation, because they're different - +, *, :, and |) When you say
> I also would control for 'LSD is the first thing exactly as often as the test"
I don't even know what I would be controlling here, since I don't know what the order is supposed, what the 'test' is, and so on. You may think your suggestion is clear, but to me it's as clear as mud.