You are looking for a pressure sensor which is a few inches square, and which can send an electronic value indicating the amount of pressure where a finger touches at any spot on its surface...
That is a tall order.
The closest thing might be a proximity (capacitance) sensor. Perhaps a sheet of aluminum foil which is connected to an oscillating circuit. Spread a sheet of insulator over the foil (cloth, etc.). The tighter a finger holds the wheel, the closer it gets to the foil, and the more it changes the oscillating frequency. It will require some experimentation.
Another possibility. In a Radio Shack book, Forrest Mims described a pressure sensor made from a piece of flexible black foam that IC pins are embedded in to reduce static charge. Its resistance is supposed to go down when it is held between conductive plates, and squeezed. Some pieces of the stuff are more rigid than others.