pg_dump and grants to PUBLIC

Hi,

I have had this problem for a while, and have not been able to find
anything in the archives or on search engines:

If I want to back up a client's database on our shared web server, I
would type:

pg_dump <database_name>

Since we are running a shared server, and since crappy (only because of
this problem) off the shelf database open source software such as
oscommerce, or phpBB2 grants access to public rather than the web user
"www" or "nobody", when I do a pg_dump for a database, I get all the
databases on the system that grant to PUBLIC being dumped with with
database that I want.

To restore, I need to go in and prune out all the extra junk that was
granted to PUBLIC by other users in other databases - very time
consuming.

How can I use pg_dump to get JUST the database in th argument, and not
other tables and databases that have granted to PUBLIC?

Altering my client's software to grant to "nobody" is not practical.

Thanks in advance,
Blair.