One method is to make them complete "simple" tasks with their non-dominant hands, like coloring. They get so excited when I pull out coloring pages and crayons, until they find out they have to use their "other" hands (by the way, I'm very careful to determine everyone's dominant hand well before any of these activities, so I won't have any cheaters).
From coloring I move on to more difficult tasks, such as creating a paper plate turkey! This involves not only coloring, but also cutting, gluing, and stapling. Fun, but very difficult to do with your opposite hand.
To make the project go smoother, I assemble their supplies beforehand (yep, there are those formula cans and copy paper box lids again!). In the cans (which double as their personal trash cans while working on this project) I place a little baggie of crayons, a glue stick, and safety scissors. Then in gallon-sized Ziploc bags, I place 2 paper plates, a small square of yellow construction paper, a small square of red construction paper, and two googly eyes. Then the cans and the baggies are placed in box lids, making them easy to store until I need them, and easy to pass out when we begin.
For the instructions, I play the video demonstration I created. This frees me up to help frustrated students - and also to catch the cheaters who are using their dominant hands!
When we are finished, I have a volunteer walk the big trash can around so students can empty their mini trash cans. Then someone else collects the now empty baggies, and a third student collects the cans with the scissors, glue stick, and crayons. Having only three students taking care of trash and collecting supplies is WAY LESS chaotic than having twenty-something high schoolers running around returning items.
And of course, there is also written component to the project, in which among other things students need to describe the physical, intellectual, social, and emotional benefits a child would experience from this activity. Feel free to use any and all of these resources!