I have found it much easier to feed in bulk and allow the worms to live in your tank. This is tricky if you have several inches of substrate, then the newts may not get to them. I think your idea of a feeding bowl/shallow dish under water is a great idea.
I have found this species will gorge themselves if food is available (if the temperatures are right and it is before breeding season). Any suggestion of portion control would be at best a guess. I think feeding 2-3 times a week, live black worms that will survive in the tank and be accessible between feedings, is key. If you have breeding adults that are in the process of egg laying, then small daily feedings is fine. My cynops p. females sometimes will take food while still attached to the plant during egg depositing. I'm not sure obesity applies to caudates. They have mechanisms to store extra fat in their tails as a protection during the months that food is scarce.
I know some breeders in the past were convinced newts with a lot of fat stores did not breed as well, but this may be speculation. I think trying to mimic their natural history of "feast and famine" periods is okay.
It is easy to apply mammalian or human physiology toward caudates. I think the idea of feeding is one that keepers think they need to feed them like they would their dog or cat. Daily and potion control. Obesity in mammals is problematic. My dog is called the "fury vacuum cleaner" since she does not allow any crumb to remain on the floor for more than two seconds. I have to worry about her weight because she seems to be always racking up the calories with my children sharing their snacks!
It's really bad when she comes out of the back seat of the car crunching on something...Happy Meal left overs never seem to fully make it to the garbage