I used variable to communicate to qvw standard object from extension.
Create variables in your qvw, like my case: south, west, north, east
and in your extension, I have things like
north = northEast.lat();
east = northEast.lng();
south = southWest.lat();
west = southWest.lng();
var doc = Qv.GetCurrentDocument();
don't worry about northEast and southWest, they are variables gettting from google map api.