I avoid using valuable rail space for a cup holder buy hanging one of these over the barrel in front of the forarm... http://www.firebox.com/product/5927/6-Bottle-Bike-Bag (it doubles as a barrel De-Resonator)

"We're all going to have so much [bleep] fun we'll need plastic surgery to remove our god damn smiles." - Clark Griswold

Remembering The 99
http://www.blurb.com/bookstore/detail/1163424