my $override_lib_path = "/usr/local/Perl/5.8.6/whatever";
my $backup_lib_path = "/lastresort/path/to/lib";

# look in $override_lib_path first
unshift @INC, $override_lib_path;

# look in $backup_lib_path last if
#  no match for a module name is found first
push @INC, $backup_lib_path;