"Well, actually, I feel it's a wee bit unethical to tell people a placebo-type thing doesn't work, because if they believe you, then it won't work. Which is a bit mean."
This could be a good point.
But:
There is some interesting evidence that saying something is a placebo does not reduce it's effect.
In least in patients who are highly susceptible anyway.
Honey is quite an expensive, and apparently hard to find, option.
And how ethical is it to endorse a deception?
And we can do better.
Assuming people who are considering honey are happy to consider other herbal options, butterbur (petasites hybridus) looks good.
Equally effective as non-drowsy antihistamines (thus better than placebo).
Pretty safe, can give some people an upset stomach but shouldn't be used if you have liver damage or are pregnant/breast feeding.
1000-150mg root extract a day should do it.