I think there is no tool wich can automatically cover the Google Earth costlines.
I draw them in GE and use this polygon as hole for FSXKML.
When you open GE and activate the layer wich shows the borders and names there is a tag "coastlines" (or similar, I have not the english version).
This polylines are only shown in a altitude over 300 meters.
If there was an solution to export this polygones for islands it would be a great solution to spare much time in drawing them manually. But I think they are not exact enought to get detailed coastlines.
I draw them in GE and use this polygon as hole for FSXKML.
When you open GE and activate the layer wich shows the borders and names there is a tag "coastlines" (or similar, I have not the english version).
This polylines are only shown in a altitude over 300 meters.
If there was an solution to export this polygones for islands it would be a great solution to spare much time in drawing them manually. But I think they are not exact enought to get detailed coastlines.