Did that work?!!
At this point it's just a string. 
What you need to do is set a smarter converter on it so that configman can change from a reference **to** a class to the actual class itself. See
https://github.com/mozilla/socorro/blob/master/socorro/middleware/middleware_app.py#L156

Also, I suggest you do what we did there in middleware_app.py by referencing the actual class itself (as a python thing, not a string) in the default. That makes sure it doesn't stumple on looking it up until you try to run it.