I've been doing a lot of browsing on the homebrew forums posted in the links section and found this bit of advice suggested to me by a number of members. This is a pseudo counterpressure bottle filler that works beautifully from a keg and keeps more carbonation in your beverage better than any other method I've ever seen.
It's simply a racking tube with a #2 drilled rubber stopper. These can be purchased from a homebrew supply store for just a few dollars. Remove the black piece at the base of your racking cane, and slip on the stopper.
Hook the top of the cane into your keg's tap and you're set!
As you bottle, place the base of your tube in such that the stopper is nice and snug in the mouth of
your bottle. You'll need to hold this in as you pour, which is easier said than done depending on your pressure that you've carbonated at. As your beverage is dispensed into the bottle, you'll see the flow stop, and the liquid in your bottle will show no bubbles. SLOWLY release the pressure by squeezing the side of the stopper. This is like slowly opening a 2-liter bottle, and the slow release of CO2 will be gentle and you won't lose as much carbonation.
It you're careful and cap immediately, leaving minimal headspace, you can still retain excellent carbonation levels.
A couple of things to keep in mind:
-For optimum results, be sure to keep everything very cold, the bottles, your syrup, your keg and it's contents. Gas is more soluble in a cold liquid than a warm liquid.
-The stopper fits some bottles better than others, so choose your bottles accordingly, unless you have access to a wider variety of drilled stoppers.
-Be careful about relieving pressure. Release it too fast and you'll blast soda all over your kitchen. The more agitation you have, the more carbonation you'll lose.