Generally speaking, this is what we do as well. When I'm back judge, if the ball has obviously been kicked, I want to blow the whistle, spit it out, and then be able to confirm yes/no before signaling. This means I'm blowing as the ball is approaching the uprights.
The ball is dead when it is obvious a kick try cannot score, so a blocked kick cannot be picked up and run in for two. However, if it's a kick/thud that never makes it over the line, that's the R's whistle, since I'll never clearly see the ball from under the uprights.