I love this technique! I wanted to see how difficult it would be to do the same in my PhotoFlow editor, and it was actually almost straightforward… here is a screencast that shows all the steps (no sound sorry!).
As you can see, one can reproduce all the steps of the GIMP tutorial, however every step is non-destructive (you can for example at any time go back to the bilateral blur and tweak the parameters).
Admittedly, I’m trying to advertise the features of my little hobby project 