WAN PPPoE: overriding IP assignment from the ISP

[Rampage]

Hello everyone,
i'm dealing with a weird situation (with a weird lazy provider)..

basically due to a routing issue on their side they are assigning me an IP which is null-router on my PPPoE Interface.
and they said: ok we can't fix things as of now, just statically assign this other IP to your PPPoE WAN interface.

I already noticed this cannot be done from the GUI, as in the interface settings i can't seem to find a field to specify the IP address.

the question is: is there any other way to do so?
i've noticed that other firewalls (like sonicwall/watchguards etc) can handle this and have a way to force a specific IP address on the PPPoE WAN interface.. even Windows (and i've said it all) allows the user to specify an IP address on their PPPoE miniport-WAN interface.

can anyone help me out and tell me if this can in any way be done using pfsense?
as of now i'm running an ugly work around where i put a computer to establish the PPPoE connection with a 1:1 inbound NAT to pfsense and a static WAN.
i would like to get rid of this dirty situation asap :)

till the ISP fixes it, which might take a while, considering their lazyness.