There is a discussion about this here: http://forum.unity3d.com/viewtopic.php?t=34735&sid=b7db7a2f8b373969ba16f82a6af23b4a
The script discussed above is here: http://www.unifycommunity.com/wiki/index.php?title=DrawLine
It might not work for complex drawing cases, but it might work for what you need.