Concerning heat, I think it can help, though that depends on how you are heating. A soak in a hot bath or jacuzzi is wonderful. Everything is loosened up and relaxed. A heating pad or IR lightbulb pointed at the penis, not so much in my experience.
In my mind, there are at least two things going on with this.
1) Relaxation. I’ve always gotten a lot better stretch when relaxed, and coming out of a 15 minute soak in a very hot bath certainly accomplishes that. Try stretching with and without, and you’ll discover the difference. A decently hot shower works ok also, though it isn’t the same.
2) Relaxation again, and this is a subtle difference. I don’t know how much heating contributes to the elongation of the tissues we are stretching. Heat certainly is popular in the physical therapy world. Sometimes even ultrasound is used in therapy sessions. I made my best hanging gains hanging immediately after a very hot soak in a bath. How much of that was due to general relaxation vs. temperature increase of the tissues being stretched I don’t know.
So, I say heat before PEing if you can. It obviously isn’t essential, but I think it is helpful. Likely at the least it shortens the “easing in” time, as in you can apply full stretching tension more quickly when thoroughly warmed up than when starting from cold.