What I see in a lot of commercial installations is a Yagi with a boom
that's longer than it needs to be for the antenna itself, sticking out
the "back" past the reflector. That part attaches to the mast. If you
had a very long boom, you might want to counterbalance it with
something if you did it that way, and you might want some way to
support the end of the boom, like a non-conductive line up to the top
of the mast. The feedline in an installation like that would go back
along the boom to the mast, and then down.

Cheers,
Tom