PARTNER YAHOO!S
Yes! There are Partner Yahoo!s. If you do them in a special manner (see below), this will double your falls (for example 6 turns instead of 3 for a vertical Yahoo!).

Prepare a Yahoo! close to your partner's board but leave at least one "wrong" block inbetween. Let your partner break this block to complete the Yahoo!

  

Problem is that I yet don't really know what you "additionally" need to do to make falls double...
Pawn Queen's Towers Guide gives some tips but I tried them out and didn't get double falls every time, so I assume there's something more to know.
I keep trying out and watching my videos...

  • It's really boring to get only the regular 3 falls for a vertical Yahoo!...
  • Getting 6 falls is awesome!
Thanks to woo_gwai_jai and temporarywings for their patience!

To be continued... One day I'm gonna find out...