You don't even need to do all that if you're willing to drop $17.95 Although I'm partial to analog, so I might be DIYing it!
I actually think this is an interesting concept, but it seems almost backwards in execution. Wouldn't it make more sense to sell a watch (or watch band) with built-in Magic Band functionality rather than a watch add-on for the regular Magic Band? There are people who wouldn't wear a Magic Band but will wear a watch.
But they don't cover the Mickey head. The watch piece would. The photos I saw had the watch slider worn to the side.
Seems like it ought to be possible to make a Mickey to Mickey connection work through the watch face, perhaps? How much material can you have between the "Mickeys" and still get a connection, or perhaps how much of an opening would you need in the watch "face" to allow a signal to pass through?