User blog comment:Dopp/Technical Update: March 27, 2012/@comment-166269-20120330211814/@comment--20120402203322

Honestly, I don't think this is possible at the moment in so far as I understand the flow of how values are written to the SMW database. The properties wouldn't be set at their current value until the page is actually saved so I think a factbox would be more like a mythbox.