Extension of web parameter plugin to allow dependency

The web paramter plugin seems very promising in terms of what we want to do (https://github.com/grundic/teamcity-web-parameters). But one feature that'd be very useful for us is having ability to populate the dependent dynamic param's drop-down once user selects the value of the param it depends on. I looked at the code a little bit being inspired by this post where it says it is possible. It uses packages in the closed API. So wasn't easy following it.

https://youtrack.jetbrains.com/issue/TW-36504

Can I update the web params individually. I was thinking that way just the dependent param could be updated in the 'Run custom build' dialog after user has set the other param it depends on.  How can you re-render dependent param's control in this scenario.  Also is there any documentation on closed API.