Most of the jobs right now are artsy / techy because those people are easiest to reach from our personal networks and that's where we started signing up mentors. Feel free to throw a janitor in a suggestion box, we'll try to sign one up.
I don't know any janitors in poland. But think of the possibilities. You could offer a "Janitor's day in the life" to entitled tech workers. The tagline could be "Step outside your bubble and see how the rest of the world lives."