Hi Craig 
I’m the author of said PropertyEditor and I have no idea how to do that 
That said, it was heavily based on the built-in Repeatable TextStrings property editor, so maybe you can figure something out. It’s very likely that I didn’t implement something properly (e.g. the PropertyEditorValueConverter) to support that.
More than happy to accept a PR if you (or someone else) figure out what’s missing!
/Chriztian