in Excel (2007 or newer) is there an easy way to apply **any** Excel formula on a set of datapoints before drawing a line/box/... on the chart, without using a helper column to do so?

(This is a generalization of the more specific question how to add a average line to the graph in excel 2007 or 2010. I actually also just want to show an average line, but I am interested in the general solution)