Well, thought I was done ;-)

Interesting issue - if I set the attribute to -1 per the above code (thanks again Ben), it works, but if someone attempts to then use the GUI to make a change to any of the other fields, clicking OK will prompt that the -1 is not valid. I guess if they ever do that, they could then take the opportunity to "clear" it manually, which is a valid value...is that the answer? Seems strange that one value is valid in the GUI and another only programmatically.