I've read somewhere here that it's impossible with popup2. Is there any module that can do it?

!popupdynmicfolder "$myfolder$"

This doesn't work when put on the first level, right after "*Popup !New !Popup"

Call !PopupDynamicFolder "$myfolder$" from a shortcuct or label click action or any other element which supports bang commands. You don't really create a new popup per se, you just call a bang. I struggled with this myself for a little while.

you can't put it there along with with other items

you can only have it as the only thing there

menu (an unskinnable popup module) has an 'insert' mechanism however.