They'd likely pull out some ridiculous example like they did with blood transfusions "if a Dr told you to abstain from alcohol, would it be ok to transfuse it into your veins?" remember that one?
In matters such as these, it's very normal for JWs to simply say "i'll ask the elders" or "i'll have to see what the society says"... never daring to think for themselves.
My guess is, cocoa tea would likely be ok seeing as it's a stimulant like caffeine is a stimulant. I mean, caffeine in high doses can kill too. I think the point is, one needs to be in control of their own mind and body (irony), so that's why drunkenness and getting high is a no-no.