Yup, as Luke said, we won’t be able to do that natively here - redirects are static at deploy time, and I don’t think you have a full list of hostnames. If I’m wrong and you do, feel free to make one redirect per name, like this:
https://luke.fbx.im/whatever https://app-luke.fbx.biz/path 301!
Otherwise you’d best be served by a function that can parse the original host header, or some other dynamic solution.