Although it may disfigure the instrument for resale, I've seen toggle switches or push-buttons attached with velcro to the keyboard. These are wired into a 1/4" phono plug, which is then plugged into the footswitch jack. So, in other words, instead of a foot switch, you have a "hand switch." These could be momentary (like a door bell) or a sliding switch / bat toggle if you don't wish to hold it down. Whatever suits your need.

The best location would be above the joystick, but I think that's where the assignable switches are. Maybe you could put them on the front side of the keyboard facing the player, or the outside (left side.)

Arrangers are 85% software, and 15% thoughtful ergonomics!