[c-nsp] OSPF - Prefer inter-area over intra-area

[nachocheeze at gmail.com]

We have a client with a network that's got a main hub site and two
'remote' sites.  By remote, I mean they're far enough away to have to
be connected by leased metro 1 Gb Ethernet circuits.  However, one of
the "this is just how it is" items is that the two remotes are
actually only a couple of blocks away from each other.  The client has
purchased and installed a wireless radio link (also 1Gb) between the
two sites.

So what we have right now is pretty much this:

            Area 0
          Main HUB
               /   \
              /     \
             /       \
Circuit   /         \   Circuit
           /           \
          /             \
         /               \
        /                 \
Site A------------------Site B
            Wireless

The Main Hub connects to the local enterprise OSPF area 0.  Site A was
rolled out as a non-zero stub area (let's say 'area 666'), with one of
the routers in the Hub acting as it's area border router (sending it a
default).  Site B is different legacy install, put in a long time ago,
and currently connects back to site A as a non-routed vlan trunking
interface.  The client wants to remove the trunking bits and make site
B a routed connection, and use the wireless link between A & B to back
up each remote site if either of the metro circuits break.

I've considered making site B the same OSPF stub area as site A so
that the OSPF learned default from the hub can route traffic from both
sites back to the hub if either leased circuit goes down.  That works,
but the problem with that is that since site A and site B would be the
same OSPF area, traffic between site A and site B would always take
the wireless path (intra-area routes are always preferred to
inter-area routes).  The client doesn't want that; since the leased
lines are considered "better" than the el-cheapo wireless, they want
all traffic from the remotes to come back to the hub (even traffic
that is from A-to-B) unless they can't due to a carrier circuit
failure.  Seems like what they want is something like an "on-demand
OSPF dial backup", but instead of old school ISDN, they want it to be
the wireless link.

I suppose I could redo OSPF and make both sites A and B part of the
OSPF area 0; then set a low metric on the wireless link between the
two.  But then I lose the OSPF learned default route from the hub site
that I get from the stub area implementation, and have to use static
defaults or else originate a default from somewhere else upstream
(which I'm loathe to do at this point for various reasons).

What kind of options would I be looking at?