The fastnet rock is easy -- it really doesn't matter much -- you can either place a mark on the rock or just to the other side... It won't materially change the results - it isn't like the results are being fed as waypoints into your autopilot.
The Scily Isle is a bit tougher especially if you are routing the whole race. I try to build a race note shape around the isles that allows the way out to pass inside but force the trip to the finish outside. This is one of those cases where I would like to just mark the out limit mark with a leave to port. The other option is to see how the grid routing gets around the scilies and put your mark there... (keep running grid routing checks to verify it is in roughly the correct place).