I think if you find yourself trying to optimize how a configuration file is loaded, you might be barking up the wrong tree for improvements of the code's efficiency. Do you know this to be a bottleneck? Or are you just guessing that it is? If startup time is the problem, maybe converting the script over to mod_perl could be more of a long-term solution.

I'm not saying you couldn't shave a few nanoseconds off startup time by tweaking how your config file gets loaded. I'm just saying that nanoseconds are small, and you may find microseconds and milliseconds hiding in other places instead.