how to assign ip addresses to mac addresses in speedtouch 585 v6

Greetings

I’ve got a speedtouch 585 v6 router and use it for sharing a dsl connection with neighbors. Each neighbor has an account to connect 1 computer. But some neighbors subscribe for 1 account yet connect 2 computers at the same time. So I wonder if there is a way to prevent them from connecting more than 1 computer. I read that some routers are able to assign a static ip address for a specific mac address. Can that be done in speedtouch 585 v6?
The web interface is very basic and has no firewall controls. But it seems that the router can do a lot, using telnet.

Can someone please guide me as to how to create rules using telnet, and how to assign specific IP addresses to specific mac addresses?

Many thanks in advance.