How to force Thai embassy in Phnom Penh to issue a non-B ?

Question.
We have a Cambodian national that we want to hire. The company is under the BOI regime, and we have a letter from the BOI stating that his work permit will be approved. Our lawyer says this is entirely equivalent to a WP3.
But the Thai Embassy in Phnom Penh refuses to issue a non-B visa without a WP3. All they do is point to the list and close the window when you try and speak to them about it. But a BOI company cant get a WP3, so it is impossible to meet their demand. Basically, the Thai Embassy is saying that no Cambodian national can work for a BOI company.
Is there any way to force their hand and make them address this ludicrous position?