After some searching, I found an application on the Android Market called Soundify. It allows you to customize the sounds for various events, such as docking a device, and already has some Transformer sounds built in along with Star Wars, Star Trek, and Harry Potter.
I also found two distinct Transformer sounds, and asked the developer to integrate them both into the application. One could be used for docking the keyboard, the other for un-docking it.
Here are the sound files:
Connect to Dock:
Disconnect from dock:
Excited for the Prime to get here. This is such a simple find, but it made my day