In the project Observations With ID Tips, I added this fake observation containing a link to a true observation that contains an ID tip. That’s how I proceed (in a very few cases) when Observer only allows other people to add their observations to traditional projects they have joined.
Are you going to ask me to delete this fake observation? 
I am ready to delete it, if it makes you feel better. 
I guess that some observers forbid addition of their observations to traditional projects because they are annoyed by the notifications and because iNaturalist does not provide a better Management of Notifications. It’s a pity!