Interesting network problem

[David G. Mackay]

I have a netopia 2241N dsl modem provided by my ISP (AT&T), which I
access through an ethernet port.  The unit can be configured in pass
through mode so that the public internet address is bridged, i.e. my
ethernet card is assigned the public address.  This has been working
well for some time now.

There was a network outage the other day, and when service was restored,
the gateway on the remote side had changed.  The fun part is that the
gateway is on a different class A ip net than my public ip.  I can
resolve all that by doing:
route add -net e.f.g.h netmask 255.0.0.0 dev ethx
route add default gw e.f.g.h
where e.f.g.h is the external gateway ip.
This borks up the /etc/sysconfig/network-scripts/ifcfg-ethx scripting.

Is there a better way to handle this, other than kludging things in
rc.local?

Thanks,
Dave