Just food for thought, along with compression being released through that valve in the nice billet head you will also be releasing oil onto said head. Even still I am considering such a set up for my Briggs.
Wow, that is insanely expensive for something you could build yourself from a cheap/broken spark plug and a few extra parts. A while back I had an idea to modify a spark plug by cutting some slits in the threads and attaching a little wrench to act as a leaver to open/close the plug. Never tried it though. I had a plug go loose before and black burned oil was bubbling out of the top, wouldn't that eventually clog up a valve.
Ok...us old guys used to use these oil foul adapters in our worn out engines...Wouldn't let oil get to the plug as easy and foul it out...Been awhile since I've had one in my hand but I think you could make this work by drilling a hole and making some kind of release....Might go get one and see what I can come up with....Only around $4 ...a lot better than $100 if you can figure it out!!