Hey so at first I thought you could just use mono cables all the way to your headphones and it would send the mono signal to both earbuds.

But after some googling out of curiosity....

"Mono-to-stereo adapters are pretty widely available for a couple of bucks.  They have a male plug on one end and a female jack on the other, and they let the same signal go to both speakers in your earbuds or headphones.  Your local Radio Shack will have them for about $3."

Source- http://askville.amazon.com/fin.....Id=9056946

you could probably find a DIY fix if you know how to solder.

yeah i had no clue they existed either, when i used to run my headphones to my guitar amp I could have sworn it always played mono in both ears even though it was just a mono cable. it could be something as simple as the size of the metal on the female end of the cable being able to hit both left and right portions of the headphone jack.

glad I had something to offer been asking questions non stop lol