Question regarding redundant paths in multi agency environment.

I am working on a project where I am connecting two agencies. Each agency
has 20+ routers. One runs RIP v1, the other EIGRP. They will be connecting
together via two PtP T1's. Each T1 is located at a different site. One T1
is going to be the preferred path, the other is simply in place as a backup
if the primary path fails. Now, a routing protocol running between the two
would make this simple, redistributing RIP into EIGRP would make this
simple, but the customer is placing a PIX 515E behind each T1 since politics
dictate the companies will be seperate security boundatries and only
explicit traffic will be forwarded between the two. They also do not wish to
route together anyway. Any thoughts on how to accomplish this? I was
considering using equal cost statics but that seems messy.

 

To clarify, I am not sure how I can get this done because the routers
connecting the two networks are in front of firewalls, so internal routers
won't be able to detect link failures or route failures since they aren't
communicating with the perimeter routers.