If you don't want to pay ZUS and don't want to break the law. Register and don't pay ZUS. If you you can't make enough for living and paying tax you can close down the business and file for bankruptcy .
That has to be the worst advice I have ever seen, specially since it is coming from someone with the name "UncleGoodAdvice".
Have you considered the fact that once he has filed for bankruptcy, he might as well just leave Poland because there won't be anything left for him here?
Your plan not to pay ZUS and if they come just to file for bankruptcy is for fools. You may have noticed that the OP has mentioned a child in his first post of this thread. Wrecklessness on the level as you have suggested is not an option anymore.
@ Schmiznurf, why don't you try to estimate your potential earnings first? Contact language schools etc. to check what they can offer you in terms of work. Registering yourself without at least having some kind of idea of what you might be able to earn is pointless in Poland. Once you register, the only people who know exactly what they will earn are the good people of ZUS and they will come for it one way or another.