Here's something Blizzard has kept well-hidden:
There is an online copy of the install files for users that purchased the game online (an option later removed for unknown reasons). It is distributed in the same method as patches, so unless you happen to own a copy of NetLimiter 2 Pro*, you're going to have to deal with a bit of lag. Anyway, you can get the files easily this way and it works flawlessly. As of the date of this post, you will only need two patches after installing BC to get it running.
*NOTE* It may be possible to skip step one; seems like it may include both BC and WoW, but I'm not sure. If so, then we have an easy project here

Here are the download links (in order of installation):
1.
WoW Downloader2.
BC Downloader3.
2.x to 2.34.
2.3 to 2.3.2If you get your AutoIt script working, let me know...I'm in need of the same thing and I'm sad that Blizz doesn't give us an easy way to do this.
The blizzard downloaders required a login to download them, so I reposted on my site (currently under construction, and will be for a while

)
Enjoy, and good luck!
* NetLimiter 2 Pro has a free trial version available for download on their site. However, the functionality is limited. You will have to register the program in order to gain the functionality mentioned in this article, although free registration info isn't hard to come by for anything nowadays...I blame Anakata...