I'm the guy from reddit previously mentioned in this thread.
@screeg: The private key you generate will import an L-address after you run it in Litecoin-qt. You need to follow it with the addwitnessaddress command, which should then output the correct M-address in your console, and add it to the wallet.
Once that's done, you need to close Litecoin-qt and open it again with the -rescan option. If you're on Linux:
<path-to-Litecoin-qt> -rescan in a terminal
If you're on Windows, create a shortcut to the Litecoin-qt application, right click, edit the properties, and add -rescan to the end of the target.
If you're on OS X, run
<path_to_Litecoin-qt.app>/Litecoin-Qt.app/Contents/MacOS/Litecoin-qt -rescan in a terminal
Feel free to message me on reddit if you/anyone else has any issues and chances upon this thread. I'm devbitcoin on reddit as well.
I will post a link to my profile here on /r/devbitcoin as proof that I'm actually the same person.