I spent a bunch of time searching tutorials and other various websites, trying to figure out how to replace the php file() function with cURL. Then I found the admin/includes/functions/localization.php file, which seems to be what this is based on. I just cut and pasted that code into the currency_update.php file, and it seems to have just updated my currencies okay on my server with allow_url_fopen disabled. Here it is if anyone wants to poke at it. I'm certainly not going to put it up on the Downloads page until someone who is more knowledgeable about these things checks and makes sure nothing is going to explode.
Currency Update (cURLed)
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