There is no direct way which i know but the below steps works for me.
# db
=> \a
=> \o /tmp/running-config
=> select value from device_config where timestamp = <some epoch timestamp> and ap_id = <controller_id> and name = 'config_template';
=> \q
The config of device with ID mentioned in the query will be exported into a file ( running-config) under the temp directory.
This however is not a flash backup sort file, its just the configuration in text format ( a template is a better word)