Personally, I don't think I've ever needed to use/require a single, specific module whose name is not known when I write the code, so I've never had cause to do quite what your examples illustrate.

When I am loading modules which can't be pulled in with just a plain, eval-free use, I'm grabbing everything in the Foo::Bar::* namespace (they're usually plugins or something similar), so I use Module::Pluggable to handle it:

  use Module::Pluggable instantiate => 'register',
                        search_path => ['Foo::Bar'];
  {
    my @plugins = plugins(undef, $hooks);
  }
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