Note : TO USE THIS .BLEND YOU NEED A RECENT BUILD OF BLENDER 2.63 (LATER THAN 46200). IT DOESN'T WORK WITH THE OFFICIAL RELEASES of 2.63a YET.
This .blend file contains nodegroups that fake volumetrics using the lightpaths ray length output. It contains a variety of materials that do this. They only produce absorption without any scattering. One is based on physical settings and is used for a variety of liquids including cola, water, merlot, apple juice, cranberry juice, budweiser, chardonnay...etc. The settings for these were taken directly from the website http://www.home.no/faenskap/3d/scattering-properties-of-participating-media.html and any other physical absorption coefficients can be used. Also included are, plain absorbing volumes (without refraction), emitting volumes, glowing glass, a simple glass shader that transmits one colour and a creative glass shader that allows any colour for various depth. I have also added a simplified way of setting realistic absorption, with a material that uses a colour at depth setting.