@Alec Logie - I used to be able to do this with my Consultant Plan as long as Day Passes were enabled. However, this is no longer working - now I am greeted with:

However, I am still able to add non-team members to a board as a Free license user with view only access (which I just did with you, Alec as a test):
 

Thanks @Robert Johnson.  Now that I’ve started to type an email on the share board screen, I can see the permission options pop up, and any users I add with View Only appear an non-team members, adding the screenshots below in case anyone else is as clueless as I am 

@Alec Logie - Thanks for sharing the screenshots. So, I tested this again and was able to add you to one board without the message I received before. Weird.