I like the approach selwin is suggesting, it would allow to unify all additional implementations under single ext module or even allow for providing injection from external modules.

```python
def import_from_module(name):
    try:
        parts = name.split(':')
        _tmp = __import__(parts[0], globals(), locals(), [parts[1], ], 0)
        return getattr(_tmp, parts[1])
    except ImportError as e:
        log.debug('Could not import from module: %s' % e)
```

something like class='path.to.woker:MyWorker' could work pretty well