Duplicate of this thread: http://www.excelforum.com/excel-char...at-origin.html
What about the proposed solutions in the previous thread do you not like?
I do note that, since you are using a line/stacked column chart (which will have a category axis), what does 0,0 mean? It might be more difficult, but an XY scatter/stacked column combination chart might be more meaningful when generating the trend line.
Or perhaps generate the trendline(s) in the spreadsheet (using the LINEST() or TREND() functions), and add those columns as additional line chart data series. The spreadsheet might look like: