You can setup a custom ModelChoiceField
that will return whatever label you’d like.
Place something like this within a fields.py or wherever applicable.
class UserModelChoiceField(ModelChoiceField):
def label_from_instance(self, obj):
return obj.get_full_name()
Then when creating your form, simply use that field
UserModelChoiceField(queryset=User.objects.filter(is_staff=False), required = False)
More info can be found here