auto_include_deps requires me to use build_requires. This means I have to know which Module::Install extensions my Makefile.PL uses. This breaks the philosophy of Module::Install. Instead, I'm doing this:

requires        ( 'perl' => 5.00503 );

# For some reason, Module::Install doesn't detect dependent modules of
# extensions. :(
Include_Dependencies_Of_Extensions();

...

sub Include_Dependencies_Of_Extensions
{
  # These don't have non-core dependencies (presumably)
  my @module_install_modules = qw(
    Module::Install::AutoInstall Module::Install::Base Module::Install
+::Build
    Module::Install::Bundle Module::Install::Can Module::Install::Fetc
+h
    Module::Install::Include Module::Install::Inline Module::Install::
+InstallDirs
    Module::Install::Makefile Module::Install::Makefile::Name
    Module::Install::Makefile::Version Module::Install::MakeMaker
    Module::Install::Metadata Module::Install::PAR Module::Install::Ru
+n
    Module::Install::Scripts Module::Install::Skip Module::Install::Wi
+n32
    Module::Install::WriteAll
  );

  foreach my $included_file (<inc/Module/Install/*.pm>,
    <inc/Module/Install/PRIVATE/*.pm>,<inc/Module/Install/PRIVATE.*pm>
+)
  {
    my $module = $included_file;
    $module =~ s#^inc/(.*)\.pm$#$1#;
    $module =~ s#/#::#g;

    next if grep { $_ eq $module } @module_install_modules;
    print "--> Including dependent modules for non-standard Module::In
+stall extension $module\n";

    include_deps($module);
  }
}
[download]

Actually, now that I think about it, it might be better to just fix the bug and submit a patch. Until it's accepted, I can store the patched module in Module::Install::PRIVATE. (Although it would be nice if the author would confirm that it's a bug... sigh)