I didn't say you couldn't, was just surprised. An excavator will throw you about and make that super hard will it not? And a world of expense and complication.
Unless you are talking about a tube for mouth and low fixed speeds forwards and reverse, left/right etc or/instead combined with a head array or couple of buttons. See
https://www.youtube.com/watch?v=lwm25wJ3O2AWheelchairs use latched controls, and programming and true track or gyro assisted type setups to achieve this. Set up with low acceleration rates low turn rates etc. They are not very easy to use if you are bounced about. Not sure how easy thats going too be for a excavator due to the way they work, or a steering system in a car.