Right now, there is no way to put Ultimate Artifacts directly on a map. Also, they are random when you place the digging spot on the map. The only other way to put them in a map is to give them to a hero, either by the editor or through scripting.
So is it possible to:
1) Add Ultimate Artifacts to the list of artifacts you can directly place on the map
2) Set which Ultimate Artifact is given by digging