You didn't mention if your car is a stick or automatic, but if you didn't want to permanently modify the car (resale considerations), I would suggest acquiring an extra set of peddle arms from a boneyard that you could use together with a properly engineered and constructed set of clamps to attach them to the cars peddle arms. The dimensions and orientation of these clamps would determine not only the added extension, but vertical height of the peddles. If I were building them I would opt for machine forming, rather than fabrication utilizing welds. Billet aluminum is very easy to work, light, and strong. When bolting the two sides of the clamp together, use thread locking compound on all fastenings as security against loosening.

The accelerator peddle could also have another peddle 'stacked on it' that was a modified OEM part. This could be done with a material also easy to work such as PVC. Grey PVC is commonly available in sheet stock to 1, and can be laminated with PVC solvent glue to whatever thickness is desirable. The center of the spacing block could be hollow to minimize weight further, so that the accelerator maintains it's light feel. I would not extend the peddle more than 4 inches using this method.

If you car has a manual transition, you can extent the shifter quite easily by acquiring a stock shift rod to use as a donor. Modify the lower end to mate to the top of another. You can remove the knob on the car's rod and install the modified shifter directly atop the one in the car, or again build a machined billet clamp assembly that will help offset the shifter as needed on the horizontal plane as well as extending it's height vertically.

I haven't looked closely at the Volvo seat mounting arrangement, but I haven't seen many in my time that were impossible to retrofit hardware that increased their height. Gaining headroom for a tall person is nearly always a tougher problem. If you have power steering, change out to a smaller diameter steering wheel once the seat is higher if you need more room to swing the legs in and out. A deeper wheel hub can extend the wheel out toward the driver a few inches if needed as well. If you need to extend the column's controls stocks back to the driver as well, I would again look to the boneyard for a couple of stock donor parts. I would then experiment with heating and reforming the plastic stalks at the points of their natural bends. They look to be a form ABS molded plastic. If so, boiling water of hot air from a heat gun will do the trick.

Maybe I should make a career out of doing this stuff . . . wonder if there is any market? :-)

Sincerely, best of luck to you and your family this holiday season.

Phil G.