A good friend of mine Jim Yarrito who is the best spoke man I have ever seen, doesn't use a torque wrench either. He is good, fast, and dependable. His wheel truing stand is older than he is, and he ain't a youngster. If you tap the spokes with your wrench, they will sound either sharp or flat, and you 'tune' them to all sound the same, when your spokes are tight. You could tighten them to the torque spec you have, and the tune them by ear.
Charlie