This would have to be a factory option; its a steering wheel with a universal joint where it meets the instrument panel.
This joint would use constant-velocity technology to give you adjustable two-way loading on your muscles when you row the steering wheel back and forth to the points of the
compass - to the beat of a rhythmic cd of course.
Your abs area should benefit first but I reckon youd soon feel it down to the soles of your feet.
All this happens only when youre held up in traffic of course, but nudge-nudge, wink-wink, say no more, say no more.
So much for that half-baked factory version - how about a cheap rather more bakeable post-fittable version comprising a piece of that velvet rope they use in banks [or on coffins!] to match your cars decor, stretched across from side to side just above your head, with a midpoint mounting.
Because youre going to be doing virtual chin-ups with it when stalled in traffic or wherever, the mountings would have to be very strong, for although you couldnt use this version while driving, it might sometimes have to be able to support two, driver and a passenger, both doing pull-ups at the same time ...
Admittedly, tall people in low-roof cars might have very little range of movement but they always do dont they?