We married in my home town in the states, and everyone we invited from the UK, except for my husbands cousins, came. I figure if people really want to come, they will find a way to get there. We had about 25 friends from the UK come to the wedding. The whole thing was awesome!
Once we had that sorted out, we offered our out of town guests as many lifts, and planned journeys as possible. I sent out maps and organised meetings for everyone who came. Lucky for me, my family only live about 30 miles from New York City, so that was also a big draw as it was a built in holiday for them also.
I don't know if that helps, but thats what we did.