Unfortunately, since they're asleep in storage, you have to terrify them yourself to get a decent flavor. Fun, sure, but it's time consuming to the point it defeats the purpose of having a yu dispenser.
Sweet been paste is sweet enough without needing to increase its sweetness. I Would not eat them myself, as they look like better pets then sea monkeys.
They look pretty tiny, unless that dispenser is larger than my arm. So if they're premature yukkuri then just loud noises or tapping the side of the dispenser should freak them out enough.