What I do is boil the wort as usual, around the time I do my 15 min. additions, I'll guestimate how much volume I lost and just add some more to get to my target post boil volume. It knocks down the boil for a second, but I start the timer again once it starts boiling
I haven't listened to the Ray Daniels show yet, but I do the same as you do. Since I'm brewing 5.5gal AG batches with a 30qt stainless steel turkey fryer pot, I have to stop sparging at 24L (little less than 6 gal). At the end of my boil I always have to add water to hit my post poil volume and gravity.
Shortly before I place my immersion chiller in the pot, I'll kill the heat so the bubbling stops and I can read the current kettle volume. Then I add the chiller and turn the heat on again. Now I can calculate the amount of water to add. But I add boiling water. This will not interrupt the boil. But the main reason for boiling is the fear of hot side aeration which could happen when I add oxygen with the cold water.
Should I be afraid of HSA when I would add cold water?