iPod XL Headphone covers for Apple in-ear buds?

I realize I'm in the minority here, but I rather like Apple's in-ear headphones and only have one minor complaint about them - my left ear is, apparently, bigger than my right (or the space to the ear canal, or whatever) and my right ear is a "large". The headphone stays firmly in place in my right ear regardless of what I do (and drowns out morons on the bus), but the left one has some difficulty staying in, and the medium falls out even more easily.

Does anyone make a sort of extra-large ear cover for these headphones? I'd be very interested in purchasing a set.