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Got a small problem I'm trying think of a solution to ...
A customer has taken the "easy way" (read: cheaper) way for a
multi-office interconnection and went through a different provider. Fine
- until he had the idea of wanting a backup. Now the other provider says
"can't do". Here's where we get back into the deal, being asked if we
could provide them with a backup over ISDN BRI.
While they do use Cisco as their primary router, it has been supplied by
the other provider, so messing around with the config is a no-no (though
technically possible, of course).

Usually, I could just configure a backup interface for the primary link
(which, btw is a leased line to the central office). If it goes down, up
goes the dormant BRI and dials the central router ... once the primary
line is back, down goes the BRI and everything is back to normal.

So, now I need some idea of how to solve this w/o changing the config on
the main router. Adding a second BRI router isn't a problem, and using
it instead of the other as default gw isn't either. But how would you
solve the routing issue? I am unable to set up OSPF or any other routing
protocol on those routers. I would no appreciate having to set up a
tunnel between the (then new) BRI router and the central router due to
the packet MTU complications it could/will cause ...

Any ideas?

Tnx, -gg