there are multiple issues in the diaper scenario. the very real issue of poop everywhere and self talk. The singing reminds me that this is not really a big deal in the scheme of things. I can't change the poop situation, and have to change the diaper
I am thinking you aren't picturing what I'm trying to describe because I have no idea how it would through your center of gravity off
I'll try to get a picture uploaded but for now let me try describing again.
You sit on the floor with your knees bent and your feet out in front of you. Put him between your legs, laying down, looking at you, with his feet in your hands (so you can lift his legs and change his diaper
) Pin his arms to the ground with your feet and, if necessary, use the inside of your calves/feet to hold his upper body still. It's very gentle and practical but it may take a picture to explain