Jeff

I am not sure that I fully understand what you are trying to accomplish. But what I think I understand is that you want to route some traffic out a different Internet interface based on the subnet from which the traffic originates. If that is a correct understanding then what you want to do is to implement Policy Based Routing which uses route maps to route specified traffic differently from what is in the normal routing table.

If that answer does not sound like what you are looking for then perhaps you can clarify a bit about your environment and your requirements.

HTH

Rick