Add custom HTML project to Jenkins project page

I am developing a new Jenkins plugin that needs to render an HTML table with some dynamic information about previous builds in the Project page (see http://prntscr.com/7s7eyd ).

My plugin currently consists of my own job (sourced from FreeStyleProject) and a custom build script that can only be applied to my job. To display the html table on the project page, I modified the main.jelly file of the custom job to display my HTML table.

But now I get another requirement: I need to delete my own job and leave only the custom build step. This step should be applicable to any freestyle project. And every freestyle project containing a custom build step must render an HTML table. The problem is that I do not have access to the main.jelly file of the random assignment, so I cannot override it.

Could you please give me a hint how to add an HTML table to a custom freestyle project?