After much work, I was (already some time ago) able to finally get CGI scripts to run on OSX Yosemite, but the problem is this. Neither any of my CGI scripts nor my PHP scripts (i.e. any of those stored on my account) run as my UserID, but instead, they run as the WebServer's UserID.
Of course, as last-resort, I do have a solution I can fall on --- I can write a CGI wrapper that solves this (yes, my level of aptitude at programming really is that many degrees beyond my level of aptitude at webserver administration) --- but if there is a way to fix this problem that is built-in to the system, I would much prefer to use that instead. So if anyone knows how to fix this, please let me know.