Now that I'm thinking more about that, it should work. I personally would RTV the heck out of the valve cover you put in the rear to prevent leaks and treat it as if it were a rear (as far as never planning on using the cap).

I do see a problem tapping the cap due to clearance of the PCV valve like PRJ said in that thread, location is key. I would use the filler neck for the added clearance necessary to make that work.