Sure. You could use a guide layer for the pointer so you could see it while you drag it around, but it wouldn’t render. The expression could be pretty simple – something like this:
maxScale = 150;
maxDist = 50;
pointer = thisComp.layer(“pointer”);
d = length(transform.position,pointer.transform.position);
ease(d,0,maxDist,[maxScale,maxScale],value)
Dan