Dr. Isotope posted about this a long time ago. He took his off after seeing heat soak sitting at idle (like a red light) that took awhile to go away. I asked him about it, he said he just plugged the hole.
So I was rooting through my toolbox looking for something else, and discovered a 2" rubber stopper (I don't even remember where I got it) that just happened to fit in the hole. I used a conventional hose clamp on it, and I've been without ever since. Actually, I had two stoppers, D has one on his car too now.