Yes, you need to execute the build on a instance wunning in ap-northeast region. At this time we haven't uploaded any meta appliances to regions other than us-east, but we have a ticket to achieve this for the next version: https://issues.jboss.org/browse/BGBUILD-201.
Once you have meta appliance (or any other instance) running in your selected region - run the build as usual - we're calculating the curretn availibility zone for instance where the build is executed. There is also an availability_zone config value for EBS plugin (which is currently undocumented - my fault, will fix it soon) where you can specify the region - in your case: ap-southeast-1. But this will throw an error if you try to build the AMI for different region than currently running (AWS limitation).
Thank you for the fast response. I will continue to be patient until the 0.9.3 version is released. In the meantime I will just have to get better working with the guts of aws.