Looking For A Program To Allow Disabled User To Play Rhythm Track

Hello, my name is William Caine, and I'm currently working with the Special Orchestra of New Mexico, a nonprofit organization dedicated to setting up and promoting music performance methods that allow Special Needs individuals to play organized music. Speaking less formally, it's the Special Olympics for music.
Currently, one of the people I am working with has severe cerebral palsy (as well as some notable but less relevant intellectual disabilities). He has an eyetracker and a tablet, and can effectively “type” using his eyes. The tablet uses Windows 7, and therefor can access a majority of software.
I've seen many cheap electronic keyboards that play a simple accompaniment piece, with the chords determined in real time by pressing the root of the chord on the keyboard. I'm looking for an software equivalent here, that would allow simple rhythm accompaniment in real time by clicking on the root of the chords. Because eye trackers are less precise and the child in question cannot realistically hold still, the clickable keys would need to be fairly large. I've found the looping software used professionally tends to be very complicated. Here, simplicity is very important.
However, try as I might, I've been unable to find such a program, and honestly have been unable to figure out how to word the question to make searching on my own feasible. I was hoping someone in this group had seen a program in their experience that matches what I am looking for.

Note: if you happen to have any interest in the Special Orchestra as a whole, here's a link to the method book. http://www.specialor...es/method03.pdf