Hi Chris,
Hope you're getting well along with your setup, I can understand the situation, but weren't there 3 copies for DB in all across your farm? I haven't touched URL ReWrite to the extent that I can tell without referring to IIS documentation, but based on your requirements, you can look into this page.
I believe ARR has settings to route incoming traffic to servers, but I haven't practically tested it (remember the limitation of my CPU), but will have a look into it if I can find something out.