-Decrease serving pressure to 2psi. You might need to blow off the pressure in the keg initially.
-Take the spring part off the filler tube so it’s just hard plastic tubing.
-Jam one end of that into a picnic tap coming off the keg. This is the part that might need alteration as I’ve only ever used a racking cane shoved in there and am not sure the filler tubes are the same diameter.
-Slide a small rubber stopper around the hard tubing (I don’t know the number but it’s the one that fits a 12oz bottle mouth)
-Put the tubing down into the bottle and medium-lightly seal the bottle with the rubber stopper.
-Engage the picnic tap and the bottle should build pressure as the beer fills it, minimizing foam.
-You will have to find a balance of bleeding the pressurized air just slightly so that the liquid can fill but not foam up.