First: The creation mage in my game had the same idea and I only had said "No". I think this idea is only for "munchkins" (sry, if I stepped on some toes), so I rejected it.
But to say, if we don't reject the idea from the beginning: No part of the rulebook states, that a freshly created creature would start with his zeon reserve full (it only states, they could contain zeon, doesn't mean, they must start with zeon). I would say, the homunuculi would start with 0 zeon and could regenerated them like every mage, 1. because it doesn't contradict the rules and 2. if they would start with zeon it would like the mage would create zeon with zeon (like he would have water and use this water to get more water).
Okay, now we say, they start with a full zeon reserve. But what happens, if the mage stops maintaining the homunuculi? They disappear. And so there zeon. Now is on the GM to decide, what happens with the zeon, a mage had transfered to him. It was created out of thin air (like the homunculi), so it should also disappear like the homunuculi, but if he used it, it can't disappear? Get the mage a "backslash" (like, if you have no Ki, but you are hit with a technquie, which steals Ki-Points), or ist der no problem at all?
This where only some of my ideas/points.