I was wondering that too. If so I'd have to think he needs it. My springs move, but the most they move is a 1/4". The only problem I see is the factory ones may not fit if he's added a leaf, but hell I'm sure there's a company out there that's made one for people using extra leafs.
I would think one of those big industrial zip ties that they sell at Lowes and Home Depot would keep them from shifting. Hell maybe Mike can get him a groovy color like lime green or hot pink too.
That would work too. Check around and see if someone makes a bigger size. I'm thinking your factory ones are going to work, but you may already know that if you've still got em.