I haven't worked at the scale where dynamically scaling the load balancers themselves is the bottleneck. I think you pose an interesting question, and I'm hoping someone with more knowledge can comment on that.
I don't believe there is any way to scale out the ELB from user side; you can contact AWS support to 'pre warm' ELB's for high traffic sites before cutting over DNS to them.
http://aws.amazon.com/articles/1636185810492479#pre-warming