Lightning protection system
how can I safely bond them ...


Safely for what? For the units themselves against lightning? Or for humans operating or servicing the units? Or for the building, against fire risk?

You have no choice but to bond them correctly for humans and for the building, which means to the protective ground that's run with their power supply.

There may be other regulations in your area about cross-grounding of the electrical system protective ground and the LPS. Read that carefully before you do anything of that nature on the roof. It might be prohibited, it might be mandated. You must follow your local electrical code.

Why follow your local code, when the laws of physics are universal? Because the regulations are local, and if you don't follow them, the insurance company you thought were going to pay up when your building burns down are going to use any deviation from the local installation regulations to wriggle out of paying your claim. You may think you know better than the local regulations about lightning protection, and you may well do. But what matters, the survival of an AC unit against rare lightning, or your finances against rare building insurance claims? Not your building? The building owner may sue you if you've made his building non-compliant with local regulations.