As I said, Radius doesn't work like that. It's not supported by Mikrotik, not supported by the industry at large. You'll have a hard time finding a NAS device which will allow you to do what you want.
The HP MSM series access controllers allow it, so do Nomadix devices.
We are using them for hotspots. We have thousands of hotspots using many different brands of hardware. We have a radius solution that parses the radius requests to a specific location in our database based on the NAS-ID. This solution existed before we started using MikroTiks and thus it is unlikely that will be changed. We use the NAS-ID because we can set it to something static, and don't have to worry about IP addresses since they are often dynamic and we have other functions that use the static NAS-ID.