Not entirely sure why you want ‘no element face’ available, but I am glad you found a pretty good Python solution.
I do recommend caution when using a TaskDialog within a hosted process such as with Dynamo for Revit or any other Revit add-in as the pop-up can get buried or otherwise hidden on screen. Since you’re already using the Revit UI you might want to consider the UI noted here instead: Calling ctypes to create a custom system message - #2 by Gui_Talarico