I know that both the conditional sentences below are acceptable:

• If I were an animal, I would be a horse.

• If I was an animal, I would be a horse:

But what about this?

• It would be unwise for a person who were only a junior in the company to criticise the boss.

You could say Were a person only or Were a junior to criticise at the start of a sentence for a reversed hypothetical, but using were after the relative pronoun who sounds strange to me.