So last year I bought a set of Profile Aerobars - the one continuous piece unit that makes a loop out and back from the handlebars. I love it. I've seen a few folks on rides with a water bottle wedged in between the aerobars like it was designed for it, so I did a little research, and sure enough, Profile makes a water bottle specific for their aerobars. When I read some more about this, I realized that it has an open hole on top covered with a 'sponge' for quick filling - obviously this is geared for triathletes. I'm no triathlete, but I do like to spend a good bit of time hammering away on my aerobars. Does anyone know if there's anything out there that would work as a good 'cap' for this e-z fill hole other than a sponge?