Metawatch kinda has music controls but they can be kinda flaky. With my menu system in my modified firmware it was very easy to add. First I needed to send music messages to the watch but as you can't define your own messages i chose to use "GeneralPurposePhoneMsg" with an option of 0x42. The first byte in the payload would be the action. I used the constants already defined in MediaControl class.
I then added a Music menu to my firmware which took all of 10 minutes. This has none of the problems with the phone defined shortcuts overriding items. I'm in the middle of a refactor of the firmware and plan to have multiple home screens like the android launcher with the music controls being one.
All this code can be seen in these two commits:-
DragonFly BSD 4.8 released
10 hours ago