There is a slightly more important problem than surface to mass ratio, even were you to stick your feet to the wall (say with a strong electro magnet) you wouldn't be able to hold yourself vertical. The muscles required for this ( In fact most of the major ones) just haven't been built up to cope with that kind of stress, also the taller you are the harder it would be. see torque and Moment of Inertia. The basic idea being that because of gravity and the lever principle taller people will have more force exerted on them. More specifically half the distance from their feet to their center of mass multiplied by their total mass gives the moment of inertia.

For all the tall guys out there this is also what makes it harder for us to do pushups than the short guys.