Have a keywords field called "AddName", choose type "Use formula for choices" with your list of users you would expect, maybe a lookup of previous users of the database stored in a view called AllUsers. Add a "USE FULL LIST" option.
temp:=@DbColumn("":"NoCache""""AllUsers"1); temp2:=@If(@IsError(temp);""temp); "USE FULL LIST" : temp2
In the Input translation event of the field put this code:
@If(AddName = "USE FULL LIST" @Name([Abbreviate];@PickList([Name] : [Single])); AddName)
Lastly, tick the box "Refresh fields on keyword change" for the field.
This means that when the user selects the pull down, the list of expected names is there quickly, but if a new name is required then the user can select "USE FULL LIST" and then select a name from the slower but complete NAB list.
NB This does not work on the web.