I guess anything is "possible". It depends on how hard you want to work, and if the result is worth it to you.
Here are 3 approaches:
1. Gut the controller
Rip out all the electronics in the Jaguar controller and replace them with your own electronics that duplicate the Intellivisions button matrix.
The result would be an intellivision controller that only supported 8 directions. If the buttons are built in to the Jaguar circuit board, you would have to either cut the circuit traces or provide new buttons. In that case the Jaguar only contributes a plastic button holder to the project.
2. Internal circuit board
Some guy made a micro controller add in board that made the Jaguar controller work with usb.
The problem with this sort of solution is that the micro controllers need power, and no power is supplied to the Intellivision controller.
3. External adapter
An external Jaguar controller to Intellivision 2 adapter could be built, but this would also require a power source. This approach would require the least amount of physical hacking, and the controller could easily be replaced if it wore out.
Does this help?