My guess is drown the tobasco in sugar water so that the sweet and the spicy ingredients counter-act in yukkuri physiology for a time. (yes I know sweets make spicy stuff taste more spicy, but that's the only reasoning I can come up with)
Maybe is some sci fi over technology chemical and nannite using marvel that hides the spiciness through some method way beyond our present technical capacity, meant to react only while inside the body.
When you drink it, it feels like water or some vegetable beberage, but inside you it reacts after a few moments, like those ultra sour candies with slow action or those "poping up" candies that take a few seconds before they start acting up.
Of course all this is farfetched and beyond realistic approach, but considering we are talking about yukkuris...
Hmm.. If you could coat very small particles of capsaicin with a wax coating, and then suspend them in the liquid. Their body heat and/or digestive process strips away the wax coating and the magic begins.
I actuality have some sweet jalapeno dipping sauce that tastes sweet at first, then the spiciness kicks in. The time between sweetness and spiciness in 1 or 2 seconds at most though.
Well spicy is like meling Bitter is like *cough*SUN*cough*
So I would say coffee tortures them more because bitter is the opposite of sweet so the chemicals that make bitter things bitter and spicy things spicy react to the sweetness of the yukkuris that cause the skin and filling to cause them pain due to the yukkuris sweetness to counter react to the different flavor that the yukkuri taken in which makes them hurt. Now let me get off subject to tell something. If we could take the flavor of an object and put in a different flavor with the original flavor with the original object then there will be a flavor hybrid, but what we taste will depend on how much of the original flavor is left, how much different flavor was added, and how much of the margin of the space of the object is left that can be filled untill it is filled with 100% flavor. Even if you take all of the flavor out of the object, the skin will still have the original flavor with it.