Hi Andrew,

There are scripts that Michael has written to help with this, they are the "CloseCurve" and the "MarkOpenCurveStart" the following link explains http://moi3d.com/forum/messages.php?webtag=MOI&msg=2888.1

You can also find a number of other useful scripts and their explanation on Petr's MoI page here http://kyticka.webzdarma.cz/3d/moi/

Cheers