I got the PPOE bridge working by following Ian's instructions but instead of selecting VCMUX i had to change it to LLC in order to get a connection. Screens are below for reference. Other than disabling NAT and QoS in advanced everything else was left at default. I think i may have also deleted one of the default WAN connections under BASIC>WAN.
Note:DHCP transmission doesnt need to be ticked i was just trialing this to see if it would stop my disconnects and it didnt so you dont need to tick this.
Unfortunately its no good though as my broadband is constantly dropping roughly ever minute so i'm back on my HH4 now with the DDWRT router attached. I'll probably try some different DDWRT firmware when i get chance as theres still the possibility of the router being the problem but to me it almost certainly looks like the HG612 is the problem. I've got a second HG612 on the way so i'll also give that one a try just incase this one is faulty.
Btw I'm using the August H-Wolf build stickied in the forum, is there a later version available that i can try? Ian i noticed you mentioned latest but your link takes me to the same H-Wolf one i'm using?
Id be interested to see if you get the bridge working tickmike and if you experience the same problem with connection dropping.