Help with Crypt

So I finally got wise and created my legacy sims graveyard underground to free up precious yard space for important things like my rocket ships. Just built a small structure big enough to place a ladder, added and open archway door and constructed my catacombs below. Unexpected Bonus is that it has also really cut down on ghosts breaking all the crap in my house every night. I guess they hang out more in the crypt at night since because they think they are already in a house. But they still come by to use the computer sometimes.

But my question is, does anyone know of a way to force the urn back to a tombstone? Because it's technically inside I get Urns and I would really like to use a platform and a tombstone to simulate the idea of an raised stone tomb. I have placed some of the tombstones that come with the vampire pack for effect but would really like to option of some actual tomb stones too.