I'll be honest in saying it doesn't traumatize your bird at all, when it's over all they care about is eating. You HAVE to starve them first. I have had best success with taking food Thursday night, taking water Friday night, and caponize first thing Saturday morning.
The chick gets tied (make sure he is stretched all the way) and may struggle at first, then I like to cover there faces, it seems to calm them. They flinch with the first cut, but once you are in, they don't move much.
If you move quickly and carefully, it's really quick (under 5 minutes for me per bird, including tying them up), and it's over before they know what happened. I am sure your husband will have no problem at all! I have no medical experience and was able to pick it up no problem.
Just be sure you get the whole testie, otherwise he will still try to mate, harass the hens, and possibly fight with the roo.
Also, I have only ever done it to 5-6 week olds, never older.
Separate him when it's done and let him heal a few days (I don't use sutures, the thigh muscle holds it closed). Watch for Wind Puffs (air pockets under the skin). I pop them if they get really big to relieve the pressure.
Also, I learned the hard way that electrolytes are super important afterward to help with shock.
I am doing a few Saturday. If I can, I'll see if I can get some pics of my set up.
PS, I am to the point where I open almost every chick, just to confirm sex. If they are boys, they get the beans removed, girls just get released and go on living their lives. I don't have money for DNA testing every chick and it's helpful me to know as soon as possible what their sex is, expecially Silkies.
PPS, I think everyone uses different techniques and tools, what I do might not work for everyone. I'll see if I can tag a few other folks to see what they have to say.