Amonkie: The simplest way to do this would be to get a pair of headphones that give you the ability to set volume levels for each ear independently and give you an internal stereo to mono converter. I would suggest Philips SBC HP170 because they are nice and comfy and sound decent for their price. The only other thing you will need to do is to wear the headphones backwards since hardware stereo to mono converters only play sound on the left ear. With the headphones I mentioned, this will be no trouble. This should accomplish everything you are looking for. Oh and here is a link to a pair of the headphones I just mentioned with a couple reviews.
http://www.amazon.com/gp/product/cus...=ATVPDKIKX0DER