>I was hoping I could simply add a route to the private network via
>127.0.0.1. For example:
>
> route add 10.1.0.0 mask 255.255.0.0 127.0.0.1 metric 1


any gateway (eg 127.0.0.1 above) must be in the same subnet as the
routed address. 10.1.0.0 is not in 127.0.0.1 and the result is as seen.

On any other OS, the hostname is associated with the NIC/IP address and
*nothing* is bound to the localhost/127.0.0.1 as this is NOT a routable
address. The Windows usage of 127.0.0.1 is at best a substitution for
the Unixdomain sock type (ie local pipes).

>but specify its IP Address rather than hostname

big mistake and now you know why