This is similar to what I'm planning. I plan to have a flare nut on one end of a small section of tubing, and a female luer-lock connection on the other side. The nut can attach to either a gas post or a liquid post, and the luer-lock will accept a syringe. This way I can dose my keg with finings, coffee, spice tinctures, hop extract, etc. without having to open the lid. I'm thinking that I'll probably use the liquid post most of the time, because I can back flush with some beer to be sure all of my additives get mixed in properly.When you get it all hooked up, do a post about it, will ya? I'm curious about that as well and would like to know how it is implemented.I wonder if these can be used for speed dry hopping.That was definitely a thought of mine. I have some parts on order to rig up a keg injector, and this was one of the uses I had in mind for it
I've been wondering about this as well and thinking that something like the below might work if it was inline in your transfer tubing. I believe they accept syringes with luer lock tips.
Somebody posted a simple work around to opening the lid a few months back and I've been using it since (embarrassed that I didn't think of it, though) - venting the keg and applying ~ 2psi to keep a positive CO2 pressure, then removing the PRV and injecting gelatin (or whatever) through the hole. I do like the inline idea as a long term solution, though.