your not changing the dietry needs. your just upping the amount of food to what is better, and healthier.
you are assuming that as soon as you give one extra feed, a snake is overweight or your overfeeding when that is not true.
Add to the fact this snake is NOT in the wild, and sometimes diets of animals in captivity are altered to the snakes need and sometimes the person keeping them too.
Like you said, theyre not in the wild and not getting excersise etc in vivs..
Since when do snakes 'excersise' in nature other then when hunting or mating anyway...
Every animal in the wild does not get food offered on a plate, they go hungry near enough all the time.
Just because an animal can go on nine meals a year doesn't mean it wont benefit from more.
If you can find proper proof on why these partivular snakes should go without more than other snakes, and why they shouldnt be offered more food than they are getting in the wild (like every other snake in captivity) I will admit my ignorance.