Generic USB plug "cap" and keyring for MuVo

[beatle]

I'm interested in getting a small solid state mp3 player that will double as a pen drive. I know the MuVo will do it, and it has several other features I like as well. However, I'd like to be able to carry the "memory" part of the MuVo without toting around the battery. I'd just leave the battery compartment in my car since that's where I'd be using it 90% of the time. I just didn't want a bulky thing hanging off my keyring. It seems that I'd need a "cap" for the USB plug as well as a tiny ring to attach to my keyring. Does anyone have an idea how I might go about doing this?