The Sketchup plugin ToolsOnSurface is primarily dedicated to drawing lines and shapes on curved surfaces. However, it also works when there is no surface. When you draw on standalone edges (i.e. not connected to faces), shapes are drawn perpendicular to the edge. You can also draw shapes in the empty space by setting the Plane of drawing. Plugin Download on Sketchucation forum at forums.sketchucation.com/viewtopic.php?f=323&t=11212&p=76625#p76625