Well, Mayo Clinic says the Neuroma may sometimes be reduced by switching to lower heel shoes - in this case, skates. Expensive. Sigh.
Have you heat molded your Superfeet, in your boots with your feet on top, in the same configuration that you use them? If not, you've defeated the whole purpose of using Superfeet. If they were properly heat molded, pressure would be equalized, within limits.
(BTW, I assume the Superfeet aren't too wide - i.e., that the sides of the boot don't scrunch them up, right?. And they were the Superfeet designed for skates, not shoes - right?)
If that doesn't equalize pressure (e.g., most of the time you really shouldn't just have pressure on the ball of your foot), we can discuss tape and foam.
It is good that you have space inside to work with - but that much space is overkill. How did that happen?