AcidMods posted this amazing video demonstrating a hack that allows rapid fire of either the Wiimote's A or B button. They're selling the required parts in their shop for $10, and promise a tutorial soon. According to the forum post announcing the mod, "out of all our kits this is [by far the] simplest.."
Following the installation, turning on the turbo function is as simple as hitting a switch next to the sync button. They've even thought to put an LED under the A button as an indicator -- a touch of class.
Yes, rapid fire is cheating, but doesn't it look like fun to mow down zombies like that in The House of the Dead 3? Now that we can mod our controllers, we won't have to mod our fingers.
[Update: the video has been removed from Vimeo, but split into two and uploaded to YouTube. Hit the break for the hardware introduction!]