[VM] Filter outgoing mail

[blueman]

I would like to filter my *outgoing* mail composed in 'vm'.
I want to do this from Emacs at the last possible moment before the
email leaves emacs/vm...

Specifically, I have a perl filter that I would like to run on each
email.

What is the best way to hook into vm here. I know I could use
vm-mail-send-hook but that is a bit klugey in that I would have to first
read and that write back the region itself. I was curious whether there
are any hooks and/or functions more amenable to filtering.

Thanks!