While there's no dedicated "snitch line" as you so eloquently put it... there is the non-emergency line which you can call and give details...
They think there's no point in an HOV reporting line, since there are very few violators (the news' words, not mine...). Keep jamming up their phone lines with these calls, and we'll see how long it takes to get a dedicated line.
Don't be the next RS.net statistic - If you drink, don't drive. You'll lose your licence, and the rest of us will laugh at you.