How can we work on controlling impulsivity (especially keeping hands to oneself) in a child with ADHD (not medicated)?

depending on age. After ruling out tactile sensory issues (hypo or hyper sensitive to touch/contact), i usually play a 'force field' game with children who continually touch, grab, or hug. Then it becomes a cue for social situations, 'remember the force field'.
Point system. You can try a point system in which everyday the don't touch others then they get a point. Once they reach a certain number of points then take them to do something that they enjoy.
Effective discipline. Depending on age and many other individual qualities, it will vary greatly. I imagine that other behaviors are also difficult to control even if this is an important one. Patience, consistency and compassion will be part of any effort. Try to find a good child psychologist to evaluate the child's capacity for self-control or at least a good book. I hope you can achieve this w/out meds. Good 4 you!