EB worker - how to scale in big steps?

I have been looking at the autoscale options in Elastic Beanstalk.

I need the worker tier to go from 1 worker to 70 workers if there is enough items in the worker queue in SQS. It seemed logical to me to set up an alarm in CloudWatch based on ApproximateNumberOfMessagesVisible in the Worker queue in SQS.

I have tried setting up a cloudwatch alarm but I believe there are 2 things that are stopping me scale in big steps: 1) the alarm triggers once so the autoscale trigger happens once. The alarm never resets so I don't get incremental scaling. I guess I am mis-understanding something here. How can i keep the alarm triggering until I get the scale I need? 2) the scaling actions are adding 1 instance at a time - Is there a way to take bigger steps for example add 10 instances at a time?

I had a look in BOTO but couldn't find anything useful there either.

What is the best way to quickly scale my EB workers based on the work load that is in the worker queue?

If there is no inbuilt way to do this has anyone got a work around to scale workers based on the queue?

Many thanks, Phil