Just once, and that was with GT2. I pulled two identical 1:16.xxx laps followed by a third lap that was exactly 0.001 seconds longer. It was at an All-Stars Race at Rome Circuit.
The car? A Lotus Elise GT1, with no race mod. Considering that car slips ands slides all over tha place, I'm still surpised I was able to do so with a car in which I could never drive more than one clean lap.