Here is how to enable cgi on lighttpd and configure it in order to execute ikiwiki.cgi wherever it is located.

Note that the first part enables cgi server wide but depending on default configuration, it may be not enough. The second part creates a specific rule that allow ikiwiki.cgi to be executed.

Warning: I only use this on my development server (offline). I am not sure of how secure this approach is. If you have any thought about it, feel free to let me know.