Haha, most mid range to high end radio's have a wired remote input. You could then buy a steering wheel control interface, and some momentary contact switches and some resistors of different values. Wire up the contact switches so each one grounds through a different resistance, then wire them into the steering wheel control interface. This would take a bit of basic DC electrical knowledge, as well reading the manual of the steering wheel interface to determine how the switches need to be wired together. You may also be able to purchase a wired remote for boat radios... this would be a bit simpler to wire into the steering wheel control interface.