Currently the best way to do that on here is, start a campaign (which is free, unlimited) and ask/invite the friends to join the campaign group. You could name the campaign, "Friends of Ruben" or something like that, and of course you don't have to run a game in the campaign, you can just use it for keeping track of people & being able to message them. Hope this helps. I agree about the "Recently Played With" section being inaccurate. For me it never seems to change who's in that list on my profile.