Hi
I agree, longer shaft might cause more problems than it solves.
I too decided to move to adding weight plates from a local Gym equipment store (very cheap).
I needed to make the hole a snugger fit and discovered that a section of tube that holds the little solar powered garden lights fits perfectly (I'd kept the tube after a light got broken...I KNEW it would come in handy...It was worth it just to be able to show my better half there was a point in me keeping things...
).
I simply refuse to pay the outrageous price of commercial weights.
I added a thin layer of rubber (2 mm wetsuit type stuff) between the sandwiched weights just to be sure there would be no movements.
cheers
frank