Counter balancing a rod

Hey all, I was wondering if anyone had any creative ways to counter
balance a flipping(flippin) rod? I know I can buy that rubber boot type
thing, that you drop weights into, but I was looking for possible ways
of doing it internally in the rod. I figured Steve would have some good
insight, and I posted it here instead of approaching directly, just in
case others wanted to do the same thing :-).

Chris