Hi Brash, now that I look at it  the seam edge will be determined by the starting point of the opposite set of curves.
Similar to how a closed surface has a "seam edge", a closed curve also has a "seam point" where the start and end of the curve come together.
The next edge from that closed curve's seam point will be the one that will become the seam edge.
You can find the seam point of a closed curve by using the plugin here which will place a point object at the start location of a curve:
http://moi3d.com/forum/index.php?webtag=MOI&msg=5288.21
Unzip that and copy the files into the \commands subfolder and then there will be a new command available named MarkCurveStart which you can set up a shortcut key for.
Right now there is not an easy way to relocate the seam point of a closed curve, but if you have a symmetrical closed curve like a circle you can just rotate it around.
 Michael
