Hello,
I've read about your project. I have a list of routers that support openwrt. Sadly, I don't own a router which supports it. However, I know how to do this but I need access to a suitable router.
Another thing, wifidog and openwrt MUST be compiled specifically for that router model your client wants to use. Furthermore, there is a router model that costs around $90 that has wifidog already installed and only needs to be configured for your client.
Let me know if you'd like to talk over the details.