Tramp multi-hop on localhost: su:sudo

[Jonathan Groll]

On OS X  (perhaps not unwarranted) I'm too afraid to let my regular
user have sudo rights, so if I want to edit a file as root, I need to
first su to another user account (that is in the sudoers file) and
then sudo to root.

All works well except for tramp. I can su and edit files that belong
to another user, but still haven't worked out how to get multihop to
the root user working.

I've read the manual, on other hosts I can use tramp multihop to first
ssh into another host and then sudo to root (eg. ubuntu boxes), but
still haven't managed to get the > su> sudo hop working on my mac.

How do I do this? Is it possible even on the localhost?

Many thanks,
Jonathan