Error when calling "Update User"

I am trying to update users' profiles projects and skills attributes:

calling:

https://graph.microsoft.com/v1.0/users/me@xxx.com

with body:

{"pastProjects": ["a","b" ]}

...works fine....

but calling: 

https://graph.microsoft.com/v1.0/users/someone-else@xxx.com

with body:

{"pastProjects": ["a","b" ]}

returns

I know that there is a note in the documentation that says these fields are not accessible to the application and require delegated permissions: could someone tell me if there is another way of doing this?