[gb-users] How can I dynamically alter default routes?

[gene]

Hello,

I've been racking my brain trying to come up with a way configure our two location 
network to provide redundant access to the internet.   I can solve everything except 
what to do about getting around default routes.  

We have two locations connected by a T1.  Each location has its own internet 
connection through a GB-1000.  

Location A 
     ISP router:  A.0.1.1
    GB-1000 
         external interface::  A.0.1.2
         protected interface:   A.0.2.1 
         gateway selector routes: A.0.1.1    A.0.2.2  
    T1-router   
          LAN: A.0.2.2
          Wan: AB.0.0.1
          default route: A.0.2.1
Location B:
       T1-router 
            Wan: AB.0.0.2 
            LAN::  B.0.2.2
            default route: AB.0.0.1
        GB-1000
            protected interface: B.0.2.1
            external interface::  B.0.1.2
            gateway selector:  B.0.1.1  B.0.2.2 
        ISP router  B.0.1.1
            
I have successfully tested one side the above configuration by disconnecting the cable 
between the ISP router and the GB-1000 at location B.  Internet traffic is routed over 
the T1 to the GB-1000 at location A and out the internet and back again.  This works 
because the default routes of the T1 routers push public addresses in that direction.  
My question is, is there a way to get it to work in the opposite direction without 
manually changing the default routes in the T1 routers? 

Thanks in advance for any and all responses.  

Gene