I have seen machines that have a bar that extends just below the table and is activated by pressing it with your knee. If you are able, that could be a way to go. I'm not at all sure what machine had that available, but I wouldn't think it to be too much of a challenge to adapt the foot control in such a fashion, especially for a sewing machine repairman.
My Viking does have a button that I can set to automatically sew until I press stop, but it's just way too automatic for me and I always get into trouble when I try to use it. I haven't been motivated to use it that much to get better at handling it.
Try the knee control thing; it didn't take much pressure at all and appeared to offer all the control of a foot device.
Good luck and blessings on you for hanging in there. Keep the faith!