I was able to find the time to test out the two main ideas here—the glacee icing and the melted IMBC. They both made good glazes but I think the glacee is the one I will use, as it dried much stiffer and I think that’s what he has in mind.
I found the melted buttercream idea very interesting. I would like to try it as a glaze some other time.
Thank you to everyone who helped me figure this out! I appreciate the help.