Hi @Casey_Dwyer,
As @Bastien_Siebman said in your other thread on this topic, there are some changes coming to the membership API that I think will likely help you. See this forum thread for details.
Basically, what I’m thinking is that instead of using the Add Users to Project endpoint, you’ll be able to use the POST /memberships endpoint to accomplish the same thing, except that, as @sasha_f explains in that thread, you can set a user as comment-only when you add them as a project member! 