This page from the Univ. of Michigan Health System offers some of the most practical suggestions I've found for sneaking extra calories into food to help stave off weight loss due to stimulant medication. It's geared for college athletes (probably football players and wrestlers) but hey, who cares as long as it's healthy and it works!
http://www.med.umich.edu/1libr/aha/aha_healgain_crs.htm
some sample tips: * To 1% milk add a quarter cup of powdered milk to add both calories and protein. * To soups, add skim milk instead of water. Top with croutons and Parmesan cheese. Bean and minestrone soups have more calories than broth types of soups. * When you drink juice, you can add the most calories by drinking grape, cranberry, pineapple, or apple juice.