I think you can just set this.rotation (might be this.angle?), clientside of course. Keep in mind that actual DB NPCs have weird problems with clientside code (you usually have to reconnect or sometimes restart the game client for clientside updates to take effect).
I couldn't figure out how to do it, so instead I just moved image info of the DB npc to a player weapon that everyone has and it updates the image using the DB NPC's vars.