Once the spinner stop moving I use the weight of the hammer and forearm movement only and the sound changes to a "tink tink" sound, and I have never had one come off!
Then once I have done a few miles give me a another knock, and check between races.
Speedway shops sell the nuts with the same thread then get a flat sided socket, torque wrench etc and do them like the race teams do, I dont think you need a torque wrench just a bar, as you will be able to cross reference the bar with the torque achieved by the hammer.
There is also a firm that makes stainless steel spinners which do better than alloy on the rear when there is a lot of wheel offset.
http://www.cobraracing.com/