Dynamically set parent queue for hotspot clients

Hello.

I am running into a issue with hotspot clients sharing a limited bandwidth.
What I want to do is to be able for a guest to login with multiple devices, with the same username, and to be limited at a total of say 10M for both these devices. If the guest is only using one device (one login), then the rate at that device should be 10M. If the guest login with another device, they should share the 10M.

Now I’m doing RADIUS logins and setting mikrotik-rate-limit, but this means that both devices will have a rate limit at 10M, so a total of 20M. How can I make a dynamic queue of some sort that solves my problem?
It has to be fully automatic. If I could set a parameter somewhere that would allow this behavior, that would be awesome.