The only way I know to measure the locking or free running torque is to use a beam torque wrench. You've got to add that to the installation torque anyway. And then you might as well just use that and torque the fastener, since you've already done everything else and the wrench is right there in your hand.
I've found variation in the free-running torque, fastener to fastener, and it changes over time. So you can't assume it's just a single number and use that for everything.
Dave