You can't. The only thing you can do is add them to your Favorite Users list. Go on someones account and click the yellow star in the top right corner under the CHAT & RULES button.
Then you go to:
My Account > My Favorites > Look at the bottom.
Lets say you add me on the Meta. I will not appear on that list in RMT & Pokebase. Hopefully, Pokemaster fixes that. So for now, add your favorite users in one place.