How to deploy to autoscaling group with only one active node without downtime

There are two questions about AWS autoscaling + deployment which I cannot clearly answer:

1. I'm currently trying to figure out, whats the best strategy to deploy to an EC2 instance behind an ELB which is the only member of an autoscaling group without downtime.

By now the EC2 setup will be done with puppet including the deployment of the application, triggered after an successful build by jenkins.

The best solution I have found is to check per script how many instances are registered at the ELB. If a single one is registered, spawn a new one, which runs puppet on startup (the new node will be up to date) and kill the old node.

2. How to deploy (autoscaling EC2 behind an ELB) without delivering two different versions of the application?

Possible solution: Check per script how many EC2 instances are registered to the ELB, spawn the same amount of instances, register all new instances and unregister all old ones.

My experiences with AWS teacher me that AWS has a service for everything. So are there any services out there to accomplish my requirements and my solutions are inconvenient?