Stretching a curve with a gradient effect?

[mitcorb]

I was doing some 2d cad work using splines to form a Gothic arch. I had formed a temporary grid for guidelines to visually adjust the points and I was thinking it would be neat if after forming the curve with the control points you could "pull" on the end to stretch it with a parametric falloff effect. In other words the stretch would have a diminishing effect the farther away from the pull point. I guess another way to describe it would be proportional scaling? This way you could stretch the curve to fit into a predetermined boundary or adjust it to a new boundary.
I am also modeling the arch in Sketchup using a photograph as a texture to trace over and found that this push pin stretch effect has similar behavior to what I am describing.
This is a learning exercise doing both at the same time, but I thought there may be some value in a script that stretches polylines, arcs, curves and so on in this way. Perhaps directional scaling in Sketchup already does this?