This post has not received a reply.. I am posting to bring this post back to the top of the list and hopefully one of my followers may be able to assist..
In addition - have you reviewed - TDT: What's a Web Data Connector? - November 5, 2015 Where Tamas Foldi walks through the development of a connector? Many find this video helpful with creating their own connectors..
I hope this helps.
So all you would need to do is execute an ajax request in your WDC code, and then put the results into a dropdown as the example above shows. The only thing on the WDC side that you need to ensure is that you do that before calling tableau.submit <- that signals that you are finished with the interactive phase.
Hope that helps,