How do I use the 9-patch plugin script for Sketch to export the Imagine style assets?

[refaQtor]

I appreciated getting directed to the 9-patch-export.sketchplugin, which is in the Imagine style repo next to the imagine.sketch template, to make Sketch export 9-patch images. But, I don't understand how to use it in Sketch.
I pasted the code into a new plugin, and ran it there; it did nothing. The plugin name suggests that it would get applied on Export; it did not.
Any ideas on how to apply the 9-patch plugin for Sketch?

[refaQtor]

if it can help anyone else who comes looking...
I used ImageMagick

mogrify -shave 1x1 -path ../style *@2x.9.png
mogrify -shave 2x2 -path ../style *@3x.9.png
mogrify -shave 3x3 -path ../style *@4x.9.png