When I want to get extra close I can go ATG above my upper lip using the following method:
Lay the flat side of the blade against (touching) your lip with the cutting edge pointed upward towards the nose. The flat side of the blade is touching the lip but the cutting edge is hovering just above the moustache area a few mm's above the skin. Then begin gently sliding the flat side of the blade up and down against the lip while very, very slowly lifting the spine just a tad so that the cutting edge is lowered and
just begins to touch. The flat side of the blade is maintained against the lip providing stability so that you can just skim the cutting bevel up and down over the moustache area beneath the nose.
For me this is a more controlled and cautious version of Xman's awesome "fool's pass" method discussed here:
One Handed Shaving Technique.
Disclaimer: If it doesn't look and feel safe for you then don't do it.