Yes. Please refer to the CPANPLUS::FAQ manpage, which contains this snippet:

my $cb = new CPANPLUS::Backend;
my $conf = $cb->configure_object;
$conf->_set_ftp(urilist => [ {
    path   => '/mnt/cdrom',
    scheme => 'file',
    host   => '//server',
}, @{ $conf->_get_ftp('urilist') } ]);
[download]

You can also set the same 'urilist' in the installed CPANPLUS/Config.pm to achieve the same effect.

As for the web-based search interface, I think you can write to gbarr@pobox.com to ask a copy of the front-end code. I think a local search.cpan.org would indeed be cool.