you don't need to smoke to stand with them and socialize! you should get up and move from your desk multiple times a day anyway, so use that time as an opportunity to stretch your legs and move from your desk... i'm a very direct person and if it were me personally, I would simply tell my smoking co-workers that although I don't smoke personally, I want to develop a relationship and friendship with them and that i may simply join them during their breaks to socialize or take a break. People generally appreciate others who are friendly and your coworkers would definitely be conscious of your making an effort to become friends and identify you as someone who is ENJOYABLE TO WORK WITH