Channel balance accessory/adapter?
As has been mentioned numerous times on these boards, there are many people out there who hear slightly worse with one ear. I myself need slightly more volume on my right ear due to a malformed ear canal (only for headphones, my brain is capable of adapting to outside sound just fine). Unfortunately, not all manufacturers of audio devices seem to care about this, presumably fairly numerous (people are exposed to a lot of harmful noise these days) demographic. Personally, I find it impossible to listen to anything that doesn't have a channel balance setting and this is why it really infuriates me that so many devices don't offer this option.
I usually simply go for devices that do offer channel balance controls fe. Rockbox, Cowon; however, I recently got a new smartphone and would like to occasionally use it as a source for my listening pleasure. Sadly, the phone has no channel balance option at all.
So my question is - are there any accessories or adapters out there that one could use between the source and the headphones that would modify the channel balance? Perhaps some headphone amps have this functionality? Does anyone know of any such device?