How to show a progress report to the user in Google Apps Script?

Question

I have a simple script that will send out a bunch of emails but these take time to send and I want to show the user a scrolling window with the emails addresses as they are sent (or, a progress bar would be good too). I believe this is possible with the new User Interface Classes, but I can't get it to work. The documentation is kinda sparse.

Specifically, the problem is that the GUI window that pops up appears blank until all the emails have been sent (the script ends) and then the text appears. This happens even if I call show(myapp) after every time I update the Label.

Answer 1

Currently, the answer appears to be, "you can't".

The best I can do is change a cell in the spreadsheet but even that completely fails (the cell only gets updated once, at the end) when sending emails.

Will update as things change...