I remember the Oregon/K-State bowl game a couple years ago where that happened, but that's only one I can recall on defense. I've never seen it on offense either.
Texas v Texas A&M, around a decade ago.
I don't believe it has ever occurred on offense. Its theoretically possible but almost definitely could not happen. A player would have to block an XP, pick it up and run it ~95 yards and start Leon Lett'ing and be stripped of the ball shortly before the goal line. The player who caused the fumble would either (a) have to recover it in the field of play, run into the endzone on his own volition in some insane attempt to return the ball 100 yards for two-points (after just running what was presumably a sprint of close to 100 yards to catch the XP blocker to begin with) and be tackled in the endzone with the ball, or (b) the fumbled ball would have to go into the endzone on its own and be fallen on by either the stripper or another player on the kicking team. It'll never happen, but it technically could. Extra awesomeness if that single-point turned up to be that teams only point of the game resulting in the first modern-era football game to end with a team scoring a single-point.
The Niners were close a couple of years ago. Dawson tried from 70+ and missed wide left to end the half. It was awesome - the whole bar stopped to watch it.
I think it was the 49ers/Ravens SB two years ago where if the Ravens had squib-kicked the final kickoff, it was a legitimate possibility for a Super Bowl fair-catch kick. I was openly hoping - despite not caring who won - that John Harbaugh was unaware of the rule and did not kick deep. I maybe haven't wanted anything to happen in a sporting event not involving a team I root quite so badly. It would've been amazing. Make it or miss it, the internet would've exploded.
