In the mean time until this feature is supported there is a username valueType field, this shows the data entry user a searchable dropdown menu of all the users in the system that they have access to. Depending on how may users are in your system, the data entry user will only have to type 2-3 letters to see their user name, and because it’s from a drop down menu rather than free text there is no chance of typos.
Hope this helps!
Pete