@jeff prince and @Jamie Eden, I'm not sure if you ever figured this out, but the following worked for me:
Download Plugin and add to my plugin folder, which for me was in Applications > Vectorworks > Plugins
Do not unzip the downloaded file!
Go to Tools > Plugins >Plug in Manager
In "Third-party Plug-ins" select install, navigate to your Plugins folder & select your zipped file, then click Install.
Restart VWX when it prompts you to do so.
Now edit your workspace. You'll find the tools in generally a weirdly-named folder in the menus list. I'm seeing a folder for this tool called "panta rhei" or something similar. Added the tool to my workspace, ran it, and presto, no more Screen Plane objects.
Thanks to Peter for linking the Layer Plane plugin!