Until you can override widgets on per user group basis, does anyone know if it's possible to change the feed settings to not display the Pixel & Tonic feed in the dashboard and either set it to be blank or another feed? Maybe using a config setting?
If you're looking to do it on a per-user basis, you can change what feed the widget points to by clicking the dashboard settings icon near the top of the dashboard. You can also remove the widget entirely from there as well.
The settings for all widgets are json-encoded and saved in the craft_widgets table in the settings column.
I have just made a plugin to do a similar thing it duplicates a selected users dashboard see https://github.com/james1238/duplicateuserdashboard