Sorry perhaps i was not able to get your question properly.
Is it something related to machining?
If you need only curves in modeling then can you use this option ?
The isoparametric curve gives you straight line because the original patch is planar (the curved boundaries are the result of trimming the surface ).
In that case you need to use offset curve in face.
I'm confused. The original picture shows a tool path, so as @ScottFelber says, we have a forum for that. If this is about creating geometry, then it belongs here. Do you want this post moved to Maufacturing?