Hey Tom - I can't think of any particularly easy ways to do this. The only way might be to either bend open or hacksaw through a link or two, and the re-attach the new bottom chain to the nunchaku. When bending the links open and closed though just be careful you don't overly weaken the metal so that it might break during use.

Tom,

Go to a local Ace, Home Depot, Lowes, any major hardware store. Go to the chain section. You can find a variety of "quick links" for chain. they are an item that looks like a chain link except one side of the link is threaded with a long nut like item see the link

http://kmsinc.thomasnet.com/viewitems/quick-links/style-7350?

When you get to the hardware store you can see the different sizes they have. Obviously you'll need one with a small enough diameter to fit through the links on the chucks, AND not interfere while swinging. You will need to leave at least one link on each side of the chucks unless you want to punch out the pin that holds the link to the ball bearing unit.

Once you find the right size quick link start sizing what length apart you want your chucks. Its simple. And when you get to the store you'll see the different sizes available.

If you are afraid that the quick links may undue themselves, pick up some Loctite threadlocker BLUE.. (it comes in a red tube but it says BLUE on it)see link

http://www.loctiteproducts.com/products/detail.asp%3fcatid=10&subid=48&plid=153

If you get Loctite RED, you'll never get the nut undone.

DO NOT CONFUSE A CHAIN QUICK LINK WITH CHEAP QUICK LINKS FOR KEYS. Although this is a simple mod, Modify at your own risk.