Stephen Ash-
I'm going to elaborate on the subject a bit, but what I say will never be suported by any agency, becouse of a-- covering, so dont try any of it:
First of all you got to seperate 2 kinds of breath holding-
1) Actualy holding your breath, (like in snorkling when going down) actively with a use of a little muscle in you throat (that I can't really remebr it's name, not in english anyway). That's the danegerous breath holding, the one that when doing so you forcefully hold air inside your lungs.
2) Simply not moving air in or out of your lungs. Not by using any muscle, but in a way that you feel that the air passage is free. This is almost not danegerouse at all.
Now let's dig a bit more:
-When equalizing we hold breath.
-Let's face it, there is no danger in breath holding with empty lungs (unless you'r very deep and going up VERY fast).
I take it from your message that you'r an instructor. Therefor you'r suposed to know the basic mechanics of it, than I guess you can figure things yourself, without me saying some untraditional things here.
The issue of breath holding gets somewhat to much attention, but for new divers, that is how it should be. Profesionals can dig some more in it.
P.S-
Oh yeah, with this said, I'll have to mention that I know of someone that got air embolism just becouse of sneezing very hard during a dive, so hey, dont hold your breath.