I, too, had this problem. At 225 and 5'8", I made contact with the bolster
and was worried about the threading being worn away, letting the seat
cover come apart. So, and this was my solution, I decided that since I
didn't want to tear up the car I would instead tear down the personal bulk.
It wasn't easy, but I went on a strict, vitamin supplemented, 1 meal a day
plan. Over 6 months, I dropped from 225 to 160, and the problem went
away.

Sure, it won't easy, and I know it won't work for some folks as the problem
is not always consumption induced, but I by taking in less calories than my
body would consume during a normal day, I was able to shed the weight
pretty quickly. Added benefits are reduced blood pressure, reduced
blood sugar levels, reduced cholesterol levels (though still higher than I
want), better heart rate, to name a few.

Now, if I can only apply that same power of will to giving up the smokes.

Of course, it may just be easier to re-cover the seats every couple of
years...

Coyote