I have situations where I want to link a user to a post even though they are not the post's author.
For example, on a radio station site, I want to link presenters to shows. The shows are a CPT created by the station manager but the presenters present the shows and are registered users of the site. Some sort of parent/child relationship linking posts to users would be really helpful.
This comes up once a while, and usually, I recommend to connect the Posts thru the authorship to the users.
In your case that's not possible, this means you need a Substituting CPT that "mimics" the Users.
1. Create a new CPT and name it as example "Members"
2. Make sure this CPT features the "Author" Field which you can decide when you setup the Post Type. Having an Author makes it easier later to classify these posts
3. Add eventually Custom Fields to the CPT's to add more necessary information on the users
Then, you need to create for each user a new post in that CTP and set the user as it's author.
Fill out the Custom Fields and then connect this Post (user) to your other posts you want to connect.
This also makes it easier later in Toolset Views to actually create custom searches thru "users" even thou you will actually query Posts, which are mirroring the User data.
Does this make sense to you?
It's the only solution right now.
This can also be partially automated with CRED for example.
When a new User Form is submitted and a user created you can run a Script that hooks in the CRED Form and creates the above mirroring post automatically.
Please let me know if you need more information on this.