First of all, you need to create an Alias for each user on DHCP. This will ensure that you always have an "identifier" name for that IP/Machine.
The page looks like this and the location can be seen at the top.
Next, you have to create a limiter. Well, you have to create two. One for download and one for upload. Like so... Make sure that the Enable limiter and its children is checked.
Then create a firewall rule, with the protocol as any, the Source as your alias and then at the bottom with advanced settings, where it says In/Out pipe, put in your limiters. Like so...