I would use a wash away stabilizer so it doesn't 'shine' thorough the fabric. And you will need a small hope that you can fit in the sleeve. It won't be easy, but it is possible. Practice on old shirts that would be discarded or make some sample tubes the same width as his sleeves. If the embroidery is to be on the cuff, I'd also use a wash away stabilizer. The embroidery will be on the inside of the cuff too, but no one will see that. If you use an adhesive wash away, you won't have to hoop the cuff. Just center it and lay it on the sticky stabilizer. Again, practice on an old shirt first.