No problem 
stuatk, I can understand!
If at the moment you don't have access to the desktop version, it may indeed make the task more complicated. That said, there are always other tips to facilitate things. For example, you can install a local web server and load frames from it. Which also means that you can edit these reference files on the fly.
Here is a simple .c3p file in wich I load images located in a "test" folder.
I have added a "?unixtime" at the end of the urls to avoid cache issues.
https://dropbox.com/s/i2oyz4xqasuj1l4/test-load-localhost-image.zip
Just one more thing, the web server must agree to share its resources. For this it is possible to add the following line to its Apache configuration file (httpd.conf or its virtual version) and restart it ("headers_module" must be activated). It's a little technical sorry, but less complicated than it seems once in place.
<IfModule mod_headers.c>
Header set Access-Control-Allow-Origin: *
</IfModule>
Someone or a bot has posted a strange message just after your answer and before mine, better avoid clicking on it.