Yes,You can do it if your camera has stong enough flash..
You will need to do it manual mode. First, setup camera for long exposure. Make 1st test shot without you using following settings..
ISO 100, f/5.6-f/8, 4 sec or more (change shutter speed to get right exposire of cityline)..
When previous step is accomplished, activate your flash and prefocus on your wife, start timer and make a shot. If your faces will bee too bright, you can lower flash power, or step back from camera..
To get everything in focus you'll need to use a smaller aperture than for a typical portrait I guess, which will slow the shutter speed down. So make sure your wife keeps very still during the long exposure. You might try experimenting using 1st and 2nd curtain flash for different effects. I wonder if 2nd curtain might work best for a very long exposure..
Use Slow Sync with Aperture Priority and f/8. You may have to adjust the flash exposure but I doubt.VictorBucuresti, Romaniahttp://s106.photobucket.com/albums/m268/victor_petcu/http://picasaweb.google.com/teodor.nitica/..
You have the right idea, here is an article with some examples on 'dragging the shutter'. Although skylines are not illustrated, the conditions should give you some ideas. Do a Google search on dragging the shutter and you'll find a number of references. Practice before you take the trip & enjoy .
Use Slow Sync with Aperture Priority and f/8. You may have to adjustthe flash exposure but I doubt..
You'll probably need a smaller aperture than that to get the skyline in focus. Experiment..