Your whole invention is clever, but this part was especially helpful since it made me realize I could put a smallish (keychain-style) split ring through the hole in the Motion pen, attach it to a lanyard, and wear it around the house/office. I don't need to attach the pen to the Edge itself, but along with my potentially losing/leaving it, one of my dogs, an otherwise well-mannered pup, is a compulsive pen thief, and I have nightmare visions of her scoring a $35.00 chew toy. I've had to train myself to clip regular $1.00 pens to my collar or put them in a drawer rather than setting them down for a minute, even on a high shelf -- since her accomplice, a year-old cat, will helpfully climb up and knock pens onto the floor so the doggie can get them.

About wrist straps for a bare PE, I think if you put a strong, snug band of elastic longways around the hinge/speaker (and of course, you'd also need to hold it shut with a crossways elastic band), then you could affix a wrist strap like one of these Etsy ones with a larger split ring to the lengthwise elastic band.