P2 Theme – media_buttons – automatically attach files to post

Hi!
I’m trying to achieve that files/images uploaded via the media buttons in P2 are automatically attached to the post written. (Like with the quickpress or the new-post/new-page form in wp-admin.)

Why I want to achieve this:
I want to give users the option to use the built-in gallery feature and add multiple images as a gallery to the post. But since uploaded files are not attached to the post the “Gallery” tab isn’t showing.

It seems that the built-in wordpress forms achieve this by creating an auto-draft of the current post. Has anyone tried this before?

I already managed to hack the P2 theme for a lot of features but haven’t been successful with this issue so far. Does anyone of you have a hint/solution for this?

Thanks in Advance!