How can I enable Trackpad tap-to-click for the login window in OS X 10.8?
Turns out you can add this as a function in the Terminal:

sudo defaults write com.apple.driver.AppleBluetoothMultitouch.trackpad Clicking -int 1

That worked for me, thanks to these guys - http://forums.macrumors.com/showthread.php?t=1218257