I've tossed the add speakers idea around also, the waterproof blue tooth speakers like the JBL flip4 look like the easiest way to get tunes on the water. Just strap it on you or somewhere on the ski. I've seen people mount speakers in the mirrors, mount them in little boxes at top of the foot well, and some people actually cut round holes directly in the hull (yikes).
There's a decent selection of marine speakers out there, the big challenge is where to mount them and do you want to cut, screw and hack things up to make it work.