I'm not really sure what you're asking. Since when do adults need "ideas" to drink? I believe you should have elaborated on this question to make it a bit more precise.
Are you referring to drinking "games?".....I hope not, since you did use the term "adults." I know underage kids play games with alcohol, which is the same as playing games with their lives.
If you refer to being a responsible host (always a good idea) I would simply suggest to my guests" Because I love you and am hosting this event, please understand that I've seen to it there are 2 designated drivers here to assure your safe trip home tonight." Have fun.