Hi Trout Hunter,

Installing aftermarket heating element is possible but it's very difficult to do a clean job. It involve removing the seat upholstery and putting it back, some special tools are needed.

In my humble Canadian opinion (it's cold up there), you can simply purchase heating cushions that you plug in the lighter. They do a good job of keeping your lower back warm. They are really inexpensive so you can get one to keep the lady comfortable while you look for a better solution.