Using another command's completion function with an alias

["Benjamin R. Haskell" <zsh@xxxxxxxxxx>]

Back in March, Bart Schaefer recommended the following useful advice for 
getting 'sshfs' to use the completion for 'scp':

compdef sshfs=scp

I have several commands that I use regularly that do some setup of the 
environment or other kinds of filtering.  For example, daemontools' 
fixcrio fixes up LF line endings to emit CRLF:

Usage is roughly: fixcrio program [args]
E.g. fixcrio nc mail.example.com smtp

I managed to get the ones that are commands to work the way I want them to 
by using:

compdef commandname=-command-

I also have some that are straightforward enough to set them as 
aliases.

alias noagent='env -u SSH_AGENT_PID -u SSH_AUTH_SOCK'

But, compdef noagent=-command-  doesn't have the desired effect.  I 
instead get the completion for 'env':

$ noagent <C-x><h>
tags in context :completion::complete:-u::
    all-files  (_files _default (eval))
tags in context :completion::complete:env::
    argument-rest  (_arguments _env (eval))

Obviously my completion-fu is still in its infancy.  Is there something 
simple to fix the 'alias' version?

Also, commandname=-command- works fine for my purposes.  But, '-command-' 
is too general: for starters, it also picks up builtins and aliases.  Is 
there something better I should use?

Thanks,
Ben