Linear Trendline in a Scatter Graph/Chart in SSRS 2008

Hi,

I am looking to create a linear trendline, similar to the one in excel , in SSRS 2008.

However when i create a scatter chart >  click on add calculated series to get the trendline options , i get only about 15 formula options for the trendline , and linear isn't one of them.

Any idea as to how i could create a linear one?

Thanks in Adv