When you create a signed-addon, in essence that is what is created. An integration user (not scoped to use the UI) is created for the Add-On and granted access to Jive. The only way to interact on behalf of this integration user is via OAuth tokens that are shared upon registration. This sounds like what you are trying to accomplish, but besides that ... doing simple Run-As signing etc... as an Admin is all that is available.
See: Core V3 API - Run-As Feature & Signed Add-Ons for steps on how to sign your add-on.
Hope that helps.
Thanks again Ryan, sorry to keep you busy with questions this am
We will look into the add-on approach.