Backgrounding part of 'ssh-agent $cmd'

[Daniel Shahaf <d.s@xxxxxxxxxxxxxxxxxx>]

tldr: I have a piece of code that prompts for password and then
establishes N ssh connections in the foreground, and I'd like the
SSH connections to be established in the background.

More specifically, my workflow involves establishing several 'ssh -MNf'
connections every morning, and running a command that prompts for
a password:

    foo_ssh_preseed() {
      ssh-agent sh -x -e -c '
        ssh-add ~/.ssh/foo.id_rsa
        for h in host1 host2 host3; do 
          ssh -MNf $h &
        done
        wait
        ssh-add -D'
    }
    foo_main() {
      foo_ssh_preseed # the workaround places an 'if' around this line
      foo_internal    # prompts for password; is interactive/long-running
    }

Right now, what happens is:

   ssh-add prompts for password
   I wait while SSH connections are being established
   foo_internal prompts for password

I can avoid the delay by running foo_ssh_preseed() in a new terminal
emulator tab; or by running it directly in the same tab, ^Zing it, and
then running foo_internal (while foo_ssh_preseed is doing its work).

I'd like to remove the complication of an extra tab or explicit ^Z:
I'd like the workflow to be

    Run foo_main
    Answer ssh-add password prompt
    # No interactive wait at this point.
    Answer the foo_internal password prompt
    (Use foo; the -MNf's will finish in a second or two.)

Thoughts?

Thanks,

Daniel