If you can make this work, more power to you. It would be pretty awesome to have all sorts of custom reflective shirts or jackets. I'd make one with my name on it! ( Kidding. )

This is a bit of a long shot, but Arc'teryx makes some of the best active clothing available - their jackets are second to none, and their base layers are great, too. They do custom embroidery for reasonable prices. Reflective thread can be had, specifically for embroidery. I don't know if they'd let you send them the thread to use, or direct them on which to buy ... but it's worth a try.