Many months have gone by. Seems the WRT hardware mentioned is fundamentally a Linux project. The hardware is essentially a Linux computer with 8p8c jacks on the side and an antenna sticking out on the end.
It's just a Linux machine. As such, anything that can be done with networking can be done with this hardware (software).
Supports L2 tunneling, TLS, I don't see dot1q but I'm sure it's there somewhere (Google 'Linux vlans').
So the challenge is in determining to what extent you choose to accommodate the existing logical design (the addresses); and the time and effort it may take to configure the hardware (software) to accomplish the accommodation.
Off the top a point-to-point configuration comes to mind. Perhaps partitioned into vans, thus achieving a logical mesh topology.
Remember you'll end up configuring iptables. So again return to the decision of whether it is worth the time. It may be better to just run a Linux or BSD box for the connectivity period, and plug in a wireless device or two somewhere on the network(s). Makes more sense.
Committing to the specific hardware mentioned; you may end up with the sense that you're building 'a ship in a bottle' kind of thing.
That's my take on this. Hope things work out.
Amiel Summers