[Answered ]-How to show __str__ representations for existing Inline objects in the admin UI, but still use the form for adding new objects

Django does indeed support this. This functionality is provided by the ModelAdmin.has_change_permission method. You would use it like this:

class FoobarModelInline(admin.TabularInline):
    model = Foobar

    def has_change_permission(self, request, obj=None):
        return False

You might also be interested in the has_delete_permission method.