You can evaluate the use of Business Actions under Roles (GW_*) for disabling the ability to add/reference contacts to accounts from the add-in.
To restrict access for only some actions within a view or hide fields or buttons entirely, do the following:
1. Choose Administration Business Operations Business Roles .
2. Open the applicable business role, then choose View All .
3. Choose Fields & Actions.
4. Under Business Action Restrictions, add a row.
5. Choose an action that you want to limit or hide for this role, and specify the corresponding restriction.
For a list of the available actions that can be restricted in e-mail add-ins, use the value selection for
the name and search for "GW_*".