So you may have noticed it is not possible to use custom keyboards in the Android player on the PB. They can be installed, but you can't change the keyboard from the default one.
But my idea is this: Would it work if we changed the manifest.xml in the custom keyboard to match the package name etc. from the default one, so that the custom one would replace the default one? (Probably increment the version number so that it's an "update")
Or is this package one that couldn't be replaced?
Here's the manifest from the stock keyboard: