Just wanted to post here again, letting everyone know how it worked.

First thing I did was chop up all of the leftover cured silicone that was at the bottom of my mix and pour buckets, and liberally layered some fill to help reduce the amount of new silicone I would need. I then mixed a fresh batch of MoldMax 30 (the same stuff I used before, and poured it on top. I let it cure for a day, and it turned out perfectly. There is a slight color difference between the two layers, but it casts and demolds as a single solid mold.

Thanks everyone!