I'll chime in here and also say that the "baseball bat" technique definitely can work. A friend of mine who ran his Honda in ITC would jack up his car, stick the bat between the tire and the fender then drop the car. "Ooops! The car fell off the jack! Darn it!", then he'd do it again. "Ooops! How did that happen!?! Darn it!", then again, and again...
The joke here is that fender flares are not allowed, but if the car just keeps falling off that pesky jack...
I have 225/45-15 tires on 8" wide rims under my rear fenders after a little massaging with the "fenderizer". The same size wheel and tire fits under the stock front fenders just fine.
Fenderization:
2x4 with rounded off end.
Lift car
Mount desired wheel/tire combo.
Insert fenderizer between tire and fender, rounded end UP.
Lower car till fenderizer is pinched in snug, but not tight.
Press end of fenderizer down as far as you can.
Repeat.
Make sure to move the 2x4 fore and aft often. Don't repeat at a given spot untill you've done the full fender, then repeat all over. The result, a nicely blistered fender that is over an inch wider than stock. Minimal paint problems at all.
On mine, the paint cracked, but I think it was because I wasn't patient and I did it outside when it was kindof cold. If you do it when the paint is nice and warm, you might avoid the cracking all together.
-Josh2