I've had a similar problem very recently with downloading docsets for Xcode 5.1.1.
My job took me to a very remote place, where we use a 256kbps satellite link as our only Internet connection, and that is mainly used to transfer a substantial amount of scientific data back to our HQ, as well as for the VoIP phones. There's very little bandwidth left for any other purpose and even that is shared between thirteen people.
I can't, therefore, use the normal download mechanism from Xcode, as it would likely time out and/or fill the link completely.
What I can do instead, is to use rsync with bandwidth limit to pull files from a server at home. To do that, I had to find the URLs for the docsets.
It turns out, Xcode uses an XML file available here, which contains a list of all docsets, along with the xcode versions that those docsets are available for. This seems to be refreshed every 24 hours. You can then parse (or manually look through) this file to grab your URLs as needed and download them with wget, curl or any other client. No need for Wireshark!