I think the best way to go about this is to straight up ask the cop for a warning BEFORE he starts writing anything down, with some I'm a poor bastard SOB story. Don't lie, but also don't be afraid to sugar coat your 'i'm a poor f*cker' story.
It takes a bit of balls, but 1) you're probably never going to see the cop again and 2) it might save you a couple hundred bucks.
I've never been let off a ticket before no matter what I said, and I've gotten six but I once asked a cop to just let me off with a warning. He seemed willing but he had already started writing and tickets have serial numbers and they have to account for each one. :disgust: