Generally speaking you can use the lerp, qarp, or cubic expressions (or some combination) with your ease formula to get the value at any point within an ease. Easing formulas can be found online easings.net
Note that you'll want one for each the x and y axes.
For example, for a quadratic ease in/out
lerp(startpositiony,endpositiony,x<0.5?2*x^2:1-((-2*x+2)^2/2))
Would give you the y value between start and end positions when inputting an x value between 0-1.