Hello,

The issue with multiple choice outcomes is that the task then wont know which path to take based on your choice.

The only way i think you can achieve this would be to go the opposite way. 

My this is mean to create a task that has a single outcome (that the user doesn't know they are picking as it will be hidden) that is simply a complete action outcome, If you want to learn how to make single outcome tasks in Nintex 365 see this post 

Then what you can do is just simply add a multi choice field with all of your "outcomes" with that field you can then perform the necessary logic to progress the workflow. 

Hope this helps

Jake