Hmm, this is a great thing to explore and mess around with. Off the top of my head-
Since the Blobs are centering around the mouse position, I would calculate the distance of each blob [ Math.sqrt( (mouse.x - blob.x)*(mouse.x - blob.x) + (mouse.y - blob.y)*(mouse.y - blob.y) ) ] and use that scale the fillSize ( which is currently hard coded to 160, with the stroke aways being 20 more ).
So if any given ball is zero pixels away from the Pointer (it's right at the middle), it is at full scale ( 1.0*160.0 ) but as the distance increases, that scale goes down ( with some lower limit as your minimum acceptable value ).
That's what I would try first, but I'm sure there are other ways of doing it. Let me know if you try it out and what works for you!