Elastic bamboo should only consider bamboo instances when counting running instances

We have just been building some EC2 server images for Windows/VS2012 CI servers triggered through bamboo (see http://davidstringeratwork.wordpress.com/2012/10/04/using-atlassian-bamboo-ondemand-for-visual-studio-2012-projects-part-1/). We built an AMI image of the CI server and configured bamboo to launch that when we committed to GITHub.
We encountered a problem when we added some other, non-transient instances to help with specialist testing. At that point, our automated CI builds would no longer trigger. We were helped out by the support folks to identify that the problem related to the "number of elastic instances on your AWS account that are not controlled by Bamboo does not exceed" setting in the bamboo configuration. Once we had some more running instances we had exceeded this value so bamboo would not launch any more instances, even though the instances were for different purposes.
Support informed us that all running instances would count towards the "number of elastic instances" and gave us 3 different scenarios where it might be relevant. For our purposes, this bamboo configuration setting should just relate to instances started from AMI images that are launched by bamboo rather than all instances regardless of the AMI from which they originate. What we would like is a way of telling bamboo (or bamboo working it out) which image types it can (or has been able to) launch and only including these in the count.