Divide bone and distribute weight maps?

local306

Anyone know of a way to divide or split a bone on a rigged character, and distribute the original weight maps across the two bones? i.e.) insert an extra spine bone for more articulation.

I am a Modo user, but I am open to any technique if you know of a relatively straight forward way to achieve this.

Eric Chadwick

Is there animation already, that you need to keep?