We tried, but it’s not so easy possible, sorry. You can of course edit the existing buttons, and add new ones, but you would have to dive into the Python code here, and modify the UI script.
Blender 2.8 will come with tabs at the top instead of the dropdown box. And there you can manage your needed layouts in the way you want here. And this code will of course also find its way into Bforartists then. That’s why we stopped to investigate here.