How to add webwork action to a project panel?

I have made my own plugins (separate) with webwork actions and with project tab modules. But now I need to combine both: there will be some comboboxes and a button that make the plugin calculate statistics. I need to show it in the same project tab.

I am having trouble with both steps:

1. How to do any Java code BEFORE project tab will be shown, and generate contents of this page with info that Java code will retrieve from userManager, groupManager etc. (fill combobox with usernames).

2. How to output new info on the same page after user presses the "Calculate!" button (calculated stats for selected user).

I think I need to redefine some methods on my project panel tab (something like "renderPage").