My first thought was to try Karicare goats milk formula.
As for Neocate, its up to you what you decide to do, but one of the kids at my DS daycare is on it and as per the peads instructions, they were told to mix up to 6 teaspoons of icing sugar in with it to hide the bitterness.
So I dont think its cause the soy is loaded with sugar, more that the neocate is truely awful stuff.
Do you really want to go down this path without medical supervision?
Try the goats first...
GL