I think what you're trying to get at is something like this: https://thejavablog.wordpress.com/2010/05/28/java-service-wrapper-and-proxy/
But that's not what's really happening. When you put a URL into the upload screen, I'm pretty sure it actually routes through your browser/desktop... not a direct download via the vCloud Director node where the command is executed.
Depending on the version of vCD and the upload system, you'll need to find out how to configure a proxy for OVFTool or the appropriate client plugin. Old plugins were Java based 5.1 and previous (i think), OVF tool was around 5.5 into some of 5.6. 8.0.1 on chrome uses a new upload CSD (client support daemon).