Step 1: The 'dashboard' - a bird suet feeder
Step 2: Remove what you don't need
Open the suet feeder, and remove the chain. The chain is intended to hang the feeder from a tree or a porch.
Step 3: Mount your new 'dashboard'
Step 4: Attach your mp3 system or anything else you desire.
I used velcro cable wraps to attach my speaker system. I used wire cutters to cut out a small part of the suet feeder wire box to make it easy to clip my iPod shuffle onto this 'dashboard'. I also plan to attach my Garmin "Runner's GPS" watch whenever I want to have a speedometer/odometer/heart rate monitor in constant view.
The box still opens, so I could conceivable carry other small things that I might not want to put in my pocket.
I use rechargeable AA batteries in the speakers. I don't know how long they last, but they certainly last a lot longer than an hour-long bike ride.
UPDATE: I went for a 14 mile ride with the music playing and discovered that the speaker unit that I used did rattle a bit on bumpy surfaces. A bit of foam under the speaker unit (folded old mousepad?) would definitely cure any issues like that. The ride, by the way, was really a lot more enjoyable to me with music.