3D Voronoi - Frame

Hi at all,

I try to get a 3d voronoi structure on a surface, all works fine so far.

With the 'Voronoi 3D' and 'SurfaceSplit' I have got a lot of trimmed surfaces.

From this I want to create a frame.
 My first try was to extrude each face along its normal, doing the same with each face scaled a little bit smaller and do a 'SolidDifference'.
Problem: After the 'SurfaceSplit' each face has the same normal direction. So I can't extrude...

Next try was to do the same with an 'SurfaceOffset'...some faces worked, some not and I dont know why.

I also tried to offset the curves of each face, but grasshopper always crashed...

maybe you guys have a short look into it :)

thank you.