dynamic addressing for alias interface

[debian@padilla.net]

I just swapped DSL providers (to get a nice new adsl2+ connection) and
am now back to a dynamic IP. No real problem here, as the dsl router
supports updates to a dynamic dns system so my dns hostname still points to
my home server. The 'problem' is when I try to access the 'public'
services from my internal network. A couple of diagrams, before and
after, will make this clearer:

Before:

Inet
 |
 |
 |      Public.IP.A
DSL Router
 |      Public.IP.B
 |
 |            Public.IP.C
Linux Sarge box
 |            Private.IP.D
 |
 |            Private.Network.Containing.D
Internal network

After:

Inet
 |
 |
 |      Public.IP.A
DSL Router
 |      Private.IP.B
 |
 |            Private.IP.C
Linux Sarge box
 |            Private.IP.D
 |
 |            Private.Network.Containing.D
Internal network

Before, the only NAT was being done by the Sarge box, with some services
running on the public interface and some on the private interface.
Clients on the private network could reach the public services because
the box itself was doing the routing. Now I have port forwarding on the
DSL router sending everything to the Sarge box, but since the PAT is
being done on the way in (external interface of DSL router) the public
services (using the hostname or public IP address) are not available to
the internal clients. The workaround is to remember to access public
services as 'public IP A' when outside (traveling) and as Private.IP.C
when at home. I'm thinking that I could put an alias interface on the
external Sarge interface, assigning it Public.IP.A. Since the forwarded
requests from the internet all hit Private.IP.C, I don't think this will
cause any problems, but I thought I'd check to see if anyone has already
solved this...

Thanks in advance,
Len