I followed the instructions below that I found on XDA listed for a G3 and I now can change themes on the stock "Home" launcher with themes that I downloaded from LG Smart World. I am on Verizon. I hope this helps you:
This is how I got the theme changer working without installing Launcher Pro.
Get the application "Any Shortcut" from play store
Open the application and enter the following details
Application : com.lge.launcher2
Activity : com.lge.launcher2.theme.LGThemeChooserActivity
Action: [Keep blank]
Intent : [Keep blank]
Then : create, your shortcut is done !
Now open the shortcut and your theme chooser application will fire up.
Download LG themes from LG Smart World application (not installed by default) and start applying themes.
As for running Smart World, when I initially side-loaded it, it would time out when trying to download. A couple of days ago, an update was available for it and I can now download ever since the update was installed. It still seems a little slow and buggy, but it works, I have downloaded themes and fonts so far with no issues. Enjoy!