Completion for command-not-found "commands"

["Benjamin R. Haskell" <zsh@benizi.com>]

The very-short version of my question is: How can I dynamically get 
completion for `git rm` when what I've typed on the commandline so far 
is `grm`?  ("dynamically" meaning without defining a bunch of compdef's 
up front.)

Longer version:

A colleague of mine finally convinced me that using his 'g___' aliases 
for git commands was superior to using my 'g ___' versions.  E.g.:

==> in his ~/.bashrc <==
alias gst='git status'
alias gco='git checkout'
========================

==> vs. my ~/.gitconfig <==
[alias]
   st = status
   co = checkout
==> and my ~/.zshrc <==
alias g=git
=======================

However, I'm still convinced that I'd rather keep mine as git 
[alias]'es, rather than shell aliases (When getting slightly complex, 
git [alias]es can be shell functions).  So, I wrote the following:

valid_git_alias () {
   git config -l | grep -qF "alias.$1="
}

valid_git_command () {
   # my `awk` is better than my `zsh` for this kind of string manipulation:
   git help --all | awk '/---/ { ok=1 ; OFS="\n" ; ORS="" } /^ / { NF=NF+1 ; if (ok) print $0 }' | grep -qF $1
}

command_not_found_handler () {
  [[ $1 = g* ]] || return 1
  local al=${1#g}
  shift
  valid_git_alias $al || valid_git_command $al || return 1
  git $al "$@"
  return 0
}

This lets me do:

`gst` -- gets converted to `git st` (which is one of my git [alias]es)
`grm` -- gets converted to `git rm` (which is a built-in git command)

The problem is that I've lost shell-completion (which I had with the `g 
___` version).  E.g. `g checkout <Tab>` would complete branches and 
tags.  And, with:

_git-co () { _git-checkout "$@" }

`g co <Tab>` would behave the same.

-- 
Best,
Ben