I love this topic because it’s really the wrench in the gears of any colour management system: no matter how much CM you have, a customer could just say he doesn’t like it; and perhaps he really does see it differently than you. The PCS (profile connection space) does factor in the observer; however, it is an aggregated function of multiple human observers. This is called the Standard Observer, and it’s used to calculate Lab and XYZ values.
I guess it is, in principle, possible to generate a Custom Observer function and use that to calculate your PCS values. One could generate a Custom Observer function of her customer and build profiles specifically for that person. Your right though that this is probably impractical since the Standard Observer function does quite a good job, and even if the colours were absolutely accurate to that person’s eye, he could still say he doesn’t like it.