I grew up in restaurants and most I have worked in would do this for free just to make you happy, and some would probably balk at the idea due to ignorance or lack or knowledge, or just lack of caring/interpersonal skills.

I think maybe if you explain your needs and the reasoning behind it (a quick lesson in halal) and regarding the no exceptions for meat, etc. that would help them be more agreeable to your request. I am thinking some may be insulted you may not think their meat is good enough, but if they know that is not the case, they will not be offended.

I hope it works out for you.

As for the person who stated they thought it may be illegal, I have never heard of a law that would prevent anything like this.....