I followed the instructions on the following thread and now LG OSP works with my G3.
The relevant post on the thread:
I also installed the LG OSP APK on my G3.
Download link for LG OSP APK:
Download link for the D855 folder I created (copied from G2 folder and changed model name in all required places):
1. Copy the files from the models available that represent the best your phone and paste them into your model's folder. If it does not exist, create it.
2. Rename the xml file to your model's name, in my case it was P930, which is also the folders name (not sure if this is critical, but to be safe just do so).
3. Open the file with notepad (notepad>open or right-click then edit).
You should see these tags:
<on-screen-phone id="P930" version="2.0">
I renamed all these (there were named "720X1280"). Fill these tags with the model of your phone, again.
In short, I made a new folder named D855 and copied all the files from the D802 folder to the D855 folder.
Then I renamed the d802 xml file to d855.
I opened the xml file in notepad, did a "search & replace" for d802 to replace it with "d855".
You should do the same for your G3's model number.