If you have an Organisation Subscription you can easily add any users (if they have registered for a Free account in Text Inspector) to your Organisation. Then they can share the same full privileges as you do.
Step 1: Ask your Guest to Register for a free account at www.textinspector.com.
Step 2: Sign into Text Inspector in the top right hand corner as usual.
Step 3: On the drop down menu choose Organisation.
Step 5: At the bottom, add in the email address of your Guest and click ADD TO ORGANISATION.