Monkey patching a module on import

Question

I've got a package structure like this

mypackage
 |-- core.py
 |-- device.py
 |-- async.py
 |-- ...

The core.py defines a Command class, which handles the communication with a device. The communication is synchronous (blocking).

#core.py
class Command(object):
    #...

The device module defines a device class, which uses the Command class to provide an API for a real device, e.g. an oscilloscope.

# device.py
class MyDevice(object):
    cmd1 = Command(...)
    cmd2 = Command(...)

The async module defines an asyncronous version of Command.

# async.py
class Command(object):
    # asyncronous command implementation

Now what I'd like to to is the following:

# Note: There is no real /mypackage/async/device.py file
import mypackage.async.device
dev = mypackage.async.device.MyDevice(...) # uses asyncronous Command implementation

There are many classes like MyDevice. I don't wan't to rewrite every one of them just to switch the Command implementation. That's why I think patching would work quite nice. But it should also be explicit (different import, the user should not know that patching has been done).

Any suggestions how I can achieve this?