ofn-path-to-shape

[Ofnuts]

For /u/oranjuiced:

Using ofn-path-to-shape and ofn-âth-edits

• Create a single line path that goes from the center of your canvas to one vertex of your polygon. Then use *Shape>On segments>Polygon or spokes* and generate the polygon (using "Circumcircle). This will create the 'inner' polygon. 
  
• On that polygon, use *Shapes>On segments>Modify segments*, keep start=0 and use end=10 (for a rounding radius that will be 1/10 of the polygon side).
  
• On these short segments, use *Shapes>On segments>Circles* with Radius/Consecutive to create a small circle around each polygon vertex.
  
• Use Edit>Break path part to put each circle it is own path
  
• Make one circle path "linked", and use *Shapes>Various>Tangents>Tangents between circles* on each of its two neighbors to generate the tangents. Repeat until you have all the tangents. Clean up the extra tangents.
  
• Cut the circles using the tangents and connect the remaining arcs (the procedure is described in the help).
  

Really a couple of minutes when you know. XCF attached.