Yes I'm aware it can be done on the HG612, but not sure if it is modem functionality or router functionality as the HG612 is essentially a single port modem/router that can be used purely as a modem.
If the HG612 was ever used on ADSL, the PPPoA credentials would have been needed to be fixed as they were supplied locked and not user accessible. Hence expecting the PPPoA details to be a router function rather than modem, however, this would necessitate ATM capability on the router WAN interface.