Just touch your peghead to the wall (or the sofa) and add lots of mass if you want to see how that sounds. Even changing how hard you grip the bass will change the mass, since it's coupling too. Since you change your fretting hand position while you play, usually dead spots aren't exactly where you are fretting, but there are exceptions. You don't have to move it off the neck, just to not exactly where you are playing.
I even know a person that can make a dead spot happen when nobody else who plays the bass can. He did eventually teach James how to do it sometimes. It's not exactly a marketable skill, but it does help show that since the bass isn't playing itself, the player can make a difference.