Your argument would only apply if the secretary was explicitly employed as both a secretary and a sex worker. Because you can't order your employees to perform unrelated duties without getting various forms of pushback, especially when that duty is providing fringe benefits for the boss personally and not for the business. Landscaping is real work, but you couldn't order the secretary to mow your lawn.
If sex work is real work, what is wrong with a boss ordering a blow job from his secretary the same way he would get a coffee? It's just work.
Your argument would only apply if the secretary was explicitly employed as both a secretary and a sex worker. Because you can't order your employees to perform unrelated duties without getting various forms of pushback, especially when that duty is providing fringe benefits for the boss personally and not for the business. Landscaping is real work, but you couldn't order the secretary to mow your lawn.
Just have HR write it into everyone's duties. Anyone higher in the company can use anyone below.