Suggestions for pg_hba.conf contents needed for dynamic IP

I'm trying to establish a robust yet inexpensive method of updating an
online database (hopefully postgres) via a customer's database (Access).
The goal is to update the online database nightly via an ODBC connection.

My problem is that the customer's web site is on a virtual host, so I don't
rule it like I want to (probably a real good idea). My customer will dial
in
to his ISP and is assigned a dynamic IP. This seems to defeat the host
based access, since one can never predict what the IP will be.

I suppose I revert to password based access, but I can find zero
documentation on how to do this.

Has anyone done this? Can it be done?