the captcha hack is a function that interacts with geeklog in points where no plugin interactions were prepared, thats why its not such an easy install.
making plugin-interaction points for captcha only is a lot of work for one plugin. we would have to include this into the core code to make it work properly, meaning that we would have to take over maintenance for the additional code. This might be possible in the future, but no such effort has been discussed yet.