Backup of entire servers and roles/tablespaces

I'm just in the process of hacking pgAdmin to allow backup of entire
servers or global info (roles and tablespaces). I was using the same
mechanism as we use for pg_dump, however this doesn't work with
pg_dumpall which doesn't support the -f option to redirect output to a file.

Instead, I've been looking at separating the output and error streams
from pg_dumpall, however this won't work either because pg_dumpall calls
pg_dump to do much of it's work, and we cannot attach to those streams
through pg_dumpall.

I'm therefore toying with writing our own backup code to act as an
equivalent to pg_dumpall, but would really prefer not to do this as the
backup code is extremely important to get right of course.

Thoughts or ideas?

Regards, Dave.