Figured out the answer to the question.
file_frame.on('open', function() {
var selection = file_frame.state().get('selection');
var library = file_frame.state('gallery-edit').get('library');
var ids = jQuery('#fg_perm_metadata').val();
if (ids) {
idsArray = ids.split(',');
idsArray.forEach(function(id) {
attachment = wp.media.attachment(id);
attachment.fetch();
selection.add( attachment ? [ attachment ] : [] );
});
file_frame.setState('gallery-edit');
idsArray.forEach(function(id) {
attachment = wp.media.attachment(id);
attachment.fetch();
library.add( attachment ? [ attachment ] : [] );
});
}
});
For more details, check: https://stackoverflow.com/questions/21858112/calling-wordpress-gallery-uploader-selector-from-metabox.
To see the working code in action, see: http://wordpress.org/plugins/featured-galleries/