Foo.php

<?php

namespace Project\API {

    class Foo
    {
        // actual functionality here
    }

}

namespace {
    // wrapper in global namespace
    class Foo extends \Project\API\Foo { }
}

usage.php

<?php

include('path/to/autoloader.php');

// both work, assuming autoloader knows the
// wrapper classes exist
$foo = \Project\API\Foo();
$foo = Foo();