+1 on using Skype. I nannied through college (graduated last year, so this is recent), and was frequently trying to find jobs in my college town while I was still at home and vice versa.
I actually found that a lot of families were actually willing to make a decision after just a Skype interview. This may have been more unique to the dc area, as a lot of these families were military/traveled a lot for work and were very used to having to make important decisions from afar. In any case, requesting a Skype interview before having to travel far for an in person one is a very reasonable request.
If you can, I also always tried to give references from both locations, I felt like it showed i still had strong ties to the area, and knew how things worked locally.