Mangling PPPoE Sessions?

Hi,
I would like to add a flow mark to some PPPoE sessions on a 2.8 Mikrotik. So far I have created a new profile for the sessions I want to mark (using the local Mikrotik user database) and I have set incoming and outgoing filters. I want these sessions to be affected by certain rules in the DST-NAT firewall, but this does not seem possible. Is there any way I can mangle these sessions automatically so that I can run certain DST-NAT rules on them? Filtering by IP address is not suitable in this situation.

Thanks in advance,
Darragh.