This trick was too good not to pass up - Andrew Hill, Sales Consultant extraordinaire from Tableau, came up with this recently. Great stuff, Andrew!
The way it works is so simple and elegant. We use Tableau's built-in Size() function to filter certain sheets on a dashboard. We then use the built-in "keep only" feature on the tooltip. As the Size() changes, the sheets filter or disappear. Size() simply means "number of answers that the database gave us."