Accessing a bridged modem management address through Balance router?

Hi there, I am not an expert so I am not sure if this is feasible, but I would like to know if it is possible to access a bridged mode through its private management IP address once the Balance One is connected through PPPoE, which is assigning to the balance One a public IP address. Apparently this is not possible. The only way to do achieve so is to set the Balance One Wan interface in the same subnet as the modem.

You can specify an additional ip, look at this thread.