I would think that you could use a Qtouch sensor IC. They are normaly touch sensors, but if you use a conductive electrode with no di-electric on top, then they have proximity sensing. The sensitivity of the chip goes up as you increase the sense cap size, (you would think it would be the other way) and the max is 200nf (.2uf) so get a QT110 series chip an use a small metal sphere (isolated from ground as well as possible) as the sensor and you may get a 1' range. If you can control the flooring, a grounded matt may help out with the range by giving the person better ground coupling.