Secondary IP on WAN interface with PPPoE?

[Mic]

Greetings folks, having a bit of a problem with some config.. running a 60E with 5.4.1, and I'm trying to figure out some way to get access to the DSL router connected to the wan interface.. It's pre-configured with 192.168.1.1/24, but since the physical interface it's connected to also needs to run PPPoE, there doesn't seem to be any way to add a secondary address on it to add it to that same subnet for the local network.

I can't imagine this is that uncommon a requirement, yet the only info I can find seems to be old and essentially unsolved.  Am I missing something painfully obvious somewhere?

[Mic]

One thing I've noticed while messing around trying to find a solution.. I've created a loopback interface, 192.168.1.251/24.. On a whim, I tried pinging the modem's IP on .1 of that subnet.  Imagine my surprise when I got replies!  tried a telnet, found it connecting back to the fortigate.  Tried another address in the subnet.. same result.

So.. am I correct in assuming that it's claiming _every_ address in the subnet it's been defined in?  That seems somewhat broken to me.  Do I need to define the loopback as a /32 then add a static route for the rest of the /24 or something?