I was going to request that myself, a mod that allows you to hold hands with anyone.
Perharps a modder can find out how it works by looking at the files of missions that involve holding hands, such as Movie Tickets or Carnival Date, or errands that envolve this.
What I know so far is that the other person acts like someone you recruited. When you find two people holding hands, one of them will not respond to you when interacted with, and will cover and scream for help when attacked. Also, while using the Super Mod, I tried to recruit the person that was unresponsive while holding hands and I couldn't.
Perharps holding hands is just a different type of recruiting.