Is it possible to show the categories as checkboxes rather than a dropdown? I dug into the widget code a little and saw that there are options for the widget, but I don't see a place to set them in the admin screens, and I don't know what the allowed values might be or I'd edit the widget itself. I also found the
if($options['display'] == "dropdown" ) statement, but it appears that the
else just repeats the dropdown list instead of showing something else.
If this hasn't been implemented yet, I'll volunteer to work on it.