In a Cocoa MacOS Application that delivers a Finder Sync extension, can I create a non sandboxed XPC Service, communicate and use it?

Question

In a Cocoa MacOS Application that delivers a Finder Sync extension, can I create a non sandboxed XPC Service, communicate and use it ? If not, what are the options in both the Mac App Store and the independent distribution Scenarios ? So far, I have attempted to add a Finder Sync target to the Even Better Authorization Sample from Apple, but the XPC service only works from the sandboxed app, not the Finder Sync Extension, even if I use the method they ship that does not need admin privileges. Therefore, I have given up for the moment to ask if I am missing something important. I have the same behaviour regardless of the signature settings, either for Mac App Store or Developer ID. I am getting error 4099 - The connection was invalidated. I have found this article that is on topic, but could not succeed to make the author's solution work.