If they got zero salary, then they would have to earn their bonuses or else end up with nothing at all. Bonuses would have to be assessed in proportion to the level of achievement, with a permanent upper pre-tax limit of €100,000.
If people cannot make ends meet on an income of €100,000, then they do not deserve to be top managers.
We would need an independent body to set proper standards and to carry out annual assessments fairly. There should also be a law stating “one person, one bonus”.