First of all, get a spare HG612 from your on-line marketplace of choice. (BT will get all pissy if you unlock the one they provide).
Unlock using the guide from huawei HG612 hacking
Remove the ptm1.301 WAN connection. This is used by BT to check up on your modem.
Edit the ptm1.101 WAN connection so that it looks like:
- WAN Connection – enabled
- Service List – INTERNET
- Port Binding – LAN1
- Connection Mode – Bridge
- Bridge Type – PPPoE Bridge
- DHCP Transparent Transmission – Disabled
- WAN 802.1q – Enabled – VLAN ID: 101
- WAN 802.1p – Enabled – VLAN ID: 1
- LAN 802.1q – Disabled
- LAN 802.1p – Disabled
Connect LAN1 of the modem to the WAN port of your router and you should be good to go.
You can connect LAN2 to your friendly neighbourhood switch and access the modem with your browser / telnet to access line stats.