How to populate data from a local database in ODK Opendatakit

[justqt]

I am working on a modification of ODK Opendatakit. ODK uses XFORMS to get input from data and creates an XML instance with data. This instance is then uploaded on the server. What I want to achieve is to auto complete some data from a local database based on an input from the data capturer. For example, if an ID is entered, then that ID is verified from the local database and if it exists, then some pre-defined fields are auto completed. If the ID does not exist, then it given a message to check the ID.I got the suggestion of using a widget or another app which verifies the entry from a local database and then returns the values of the fields to be completed to the ODK XML instance. What I don't get is how do I pass the values to an instance session in ODK?