Photographer Jay P. Morgan made this informative walkthrough showing how he shot a photograph that combines artificial light with the evening sky:
[…] its a simple street light or a full on city scape this process works. We shot a scene for Pilot Freight Services using this method and got great results. We shot our background plate of the bridge and city lights and combined it with a shot done later of the truck.
It’s not exactly a project you can do by yourself, but the concepts he explain can be applied to your nighttime photography.