I think that just about solves my problem 
Is there any way to do this same thing from within an application context XML? If not, no worries, I'll just pass in an array of flashvars to my application as so:
Code:
{
'resources': [
{ 'name': "English (US)", 'locale': "en_US", 'file': "i18n/resources.en_US.properties" },
{ 'name': "English (UK)", 'locale': "en_GB", 'file': "i18n/resources.en_GB.properties" }
]
}
My main goal here is to keep resource bundles completely external from the application itself.