You can force a linear regression to pass through the origin of coordinates. The best way I have found so far it is to convert the raster to a numpy array, move the coordinate system so my origin of coordinates is the point I want to pass through, create a least square model using numpy.linalg.lstsq where Z = aX + bY + c and c = 0, and then use the model to create the raster.
I'll let you know if it works.