Yoda Power, I downloaded Lord Malbeth's gemstone unit and investigated using the Holy Relic unit in Conquests for just that very thing, but the one wasn't quite up to snuff and the other may work with the right amount of tweaking. I have not delved into PhotoShop, yet, so it may turn out I'm doing everything the long, difficult way, but for now I'm content to cut-and-paste, since I'm already very pleased with the quality of the Firaxis units -- the golden standard, as it were.
I probably won't call the finished unit a Bastilodon if it has a magic attack. It'll be called a Solar Engine or Altar of Sotek or what have you.