What I got is I use an app for gaming shortcuts called “ReWASD”.
It allows you to remap any controller, be it a keyboard, a mouse, a console controller, etc. All it needs is that your various devices are from a different make and/or model (otherwise it can’t differentiate between them). So I got another normal computer keyboard that is entirely remapped - every key is remapped to ctrl+shift+alt+key - and I use that for those less used but otherwise more convoluted functions Mattias mentioned. It works like a charm and is very very flexible. With the bonus that if you need to replace the device, you just get your saved mapping and apply that to the new device, no sweat.
I also got a Razer Tartarus Pro for my left hand, which is also remappable and has multiple layers selectable from a thumb pad. So there I have my spacebar, my modifier keys, the most used shortcuts for Spectralayers, a second scroll wheel, etc.
So my setup is: left hand on Tartarus, Right hand on the trackball, a regular keyboard for typing, etc. in the center and the remapped keyboard below it.