Just do somethin like this...
Cheap set of $7 collapsable headphones from target. removed the top head band from the set. the adustable drop bars are still there just retracted fully. slipped them out the top of the helmet help route the wires. I bound the remaining halfs togther and then bound the setup to the visor. Then, took the jack end of the wire and ran it out the back of the helmet. Ipod is held in a neoprene armband. Enough wire is used up by routing it through the helmet and the speakers being up at the front that there isn't much to get caught anywhere in back for the short wire that exists on these. Although if the wire is longer than wanted you can wrap it around the ipod band. The soft wire of typical headphones will easily snap in any accident where they catch on something firm. I still need to find a nicer way to attach them to the visor. White wire ties look very cheap.
Doesnt' block sound from the outside world nearly as bad as having them on your ears.
Incentive to wear your helmet if you dont already.
Ride with music.
No chance for them to fall off and get wrapped up in the chain/gearing.
Possible shortend life of headphones as you have to run the ipod's volume very high to get good sound level.