You can still use self-assessments, manager and peer reports on the work done, e.g. each quarter. Just explicitly don't use them for promotion. If they are used only for "whether this person brings more to the company than company spends on them", then it unlikely to become a metric to game around.

Probably based on an engaged managers evaluation of their work output

See above - it's strange to discount management techniques for promotions and pay rises, but still use it for firing people.

I think I missed the point where parent said not to use management techniques for promotion and comp. Can you highlight what you are seeing?

We're talking about leveling and compensation based mostly or entirely on years of experience; this implies they are based only a little or not at all on performance reviews.