See update below
I found the answer that worked for me.
When you plug in the phone, bring down the status shade, pick the USB item (“USB connected”) then, from there, pick “Internet connection” — I chose Ethernet, but I’m not sure the choice matters on the dialog that pops up..
This enables USB debugging to become active; leaving it on Charging, MTP, or PTP does not work.
Once you do this, you can follow @Siddharth’s steps to setting the ADB drivers, if needed. (You may need to use the actual LG drivers and not the Google drivers, but once I got this far, it was just like any other phone.)
Caveat
For me, even after going through this once, I still get the “installer” first and then have got go in and choose the “Internet connection” again. But, at least it works.
Update 10 Dec 2014
A recent firmware update has, indeed, removed the “Internet connection” as an option. Instead, PTP now works. I still get the “Connected as an installer” notification every time I plug in the phone and have to click on the notification then click on “Camera (PTP)” — or wait about a minute. It’s slightly better than what It was.
Also note: When this change occurred I had to install the drivers again for the phone, since it comes up as a different type of device when “Camera (PTP)” is chosen than when I used the “Internet connection” option.