...Okay, no-one's going to believe this. I almost don't believe it.
In an utterly unbelievable turn of fate, one of the two flashguns I acquired for this challenge is almost MHS compatible. I'm not kidding. The outer diameter of most of the body is 36.65mm/1.445", so lightly sanded MHS shrouding will fit around it, and the inner diameter is 34.75mm/1.365", which means that standard MHS male threads fit inside it with a near perfect friction fit.