Never used Sketchup so it may not be this easy, but why can't you just...
Go into Sketchup, make a box 1 Unit long in one direction, any size in the others.
Import it into NL2
Make a track segment that is exactly the length of the 1 Unit side of your object.
Check the length of the track in Coaster->Coaster Properties->Statistics.
Your scale is 1 unit = X feet where X = length of track.
If 1 unit is too small in NL2 to work with make it 10/100/1000 Units so you can work with it. Just divide Feet by how many Units you used to get feet per Unit.