I use a single dot pipper and raise the seat as far as it will go just before the pipper disappears from the top of the HUD. I consider this within the real operating parameters of the cockpit.
Drawing a dot on the screen or any other device that allows you to raise the seat higher so that the pipper is no longer visible on the HUD, I consider gamey. If you do it, I don't really care ... just not my personal preference.
For those over the nose deflection shots, prior to losing site of the target, one must understand the POM of the target and your POM before pulling lead and firing. Like Lev said, you must "visualize" for the blind shots. This is not something that comes easily or quickly for most, I would assume, and thru many hours of fighting and/or practicing the "visulaization" gets better.
How many find it easier to get deflection shots than off-center 6 shots ? Sometimes, when I have locked onto a target, I wait for the target to turn before firing (I do not do this under "furball" conditions tho).