Sid why didn't you tell me you play tabletop.
The character doesn't necessarily need Darth in front of his name, that's a preconception created by the fan-base. There were plenty of Sith that didn't have the title of Darth. However if you want him to have Darth, maybe instead of going the traditional Latin route, go the Greek route. Even if you want to stick with a Latin root, figuring out the portfolio of the character is more important, and naming based on their portfolio ends up being more engaging, even if it doesn't sound as cool initially. For instance, I DM for a dnd 3.5 group, and I have a shittonne of characters that I've thought up, including gods.
One of those gods is a demigod of Freedom, and I assigned his name in draconic(he's a half-dragon). In effect his name is draconic for Rebel, Renegade, and Free (Dragons have very long names). Once one of the players learned how to speak draconic, He was suddenly able to figure out the characters name, and it added more depth to the setting as a whole.
So based on Morbus and Scelus, and seeing as he is a sith (assuming part of the empire, which is LE,):
Darth Caprificus (Latin for Ambition, Pride, fig-tree)
Darth Vorso (Latin for Twist, turn violently, manipulate)
Darth Premo (Latin for Oppress, constrain)
Darth Epivallo (Greek for enforce)
Or without Darth:
Inperium (Government, order, ect, in Latin)
Rego (same thing)
Dictum (dictate, order, same thing really)