This seems to produce the desired behavior, but has the unfortunate side effect of a rather twitchy cursor and significant slow down (at least when running across the network) when I'm doing many updates in rapid succession (e.g. "Your job is 37% done", "Your job is 38% done", etc.)

I think a combination of using idletasks()and making sure not to (Un)Busy an already (Un)Busy widget (by keeping a global indicator of the Busy state of the widget) seems to be working the way I had envisioned (although I'm still testing).

Thanks all.