How can I shorten my female cycle to around 25-26 days?

I am currently trying to move my period a few days forward because of a huge event several months away in the winter. My cycles are fairly regular at about 27-28 days. At this point, I know I will have it on that day because my body is usually very predictable. Does anyone know of any methods (besides hormones or birth control), that could push my period ahead so it comes a little faster and my cycle length is shorter? I have heard there might be some Herbs, but I am not sure. Please help!