gistfile1.txt

<?php
    // add to the end of FactoryTest
    public function testSetterCallable()
    {
        $this->factory->setter['Aura\Di\FakeChildClass']['setFake'] = function () {
            return 'OOPS';
        };

        $object = $this->factory->newInstance('Aura\Di\FakeChildClass');
        $actual = $object->getFake();
        $this->assertInstanceOf('Closure', $actual);
    }

So, you should be able to pass that inner closure by itself to the setter, and the DI system will use that closure itself as the value for the setter. Then you can retain it as a property (or whatever) and invoke it inside the class later. Does that help?

Totally. I'll test after lunch. Probably just an overtired scope issue :-)

Get some rest man. :-)