This patch uses the steps on wiibrew.org/wiki/Wiimore/Extension_Controllers to allow unencrypted communication. This has two effects: it should allow the use of third-party extension controllers, and it makes WII_DECRYPT unnecessary.
Note: I was unable to successfully build DarwiinRemote.app (even without any changes; my changes should also not affect discovery). Although the build product looked good, it was consistently unable to connect to my wiimote. Since I only needed to change WiiRemoteFramework, I was able to get away with building only that and dropping the result into DarwiinRemote 2011-03-08-10-00.
Testing done: I have a third-party classic controller that DarwiinRemote 2011-03-08-10-00 does not detect. Built as described above, verified that the wiimote, nunchuk, and (official) classic controller (pro) still worked. Plugging in my third-party classic controller brought up the classic controller pane as expected, and I was able to play Cave Story successfully with it.
I also tested this patch combined with my other minor cleanup patch, they do work together.