If you are giving your PPPOE user a fixed IP set up a simple queue with the Target Address set to that of the PPPoE user. This will accumulate the traffic for you.
I discovered the hard way (as usual?) that even with pppoe rate limits set for each customer, simple queue’s it will override any pppoe limits set and if not set in simple queue’s will give users unlimited bandwidth, so for me for each customer I have duplicated the rate setting in both.